Signaling of deblocking filter parameters in video coding

ABSTRACT

This disclosure describes techniques for signaling deblocking filter parameters for a current slice of video data with reduced bitstream overhead. Deblocking filter parameters may be coded in one or more of a picture layer parameter set and a slice header. The techniques reduce a number of bits used to signal the deblocking filter parameters by coding a first syntax element that indicates whether deblocking filter parameters are present in both the picture layer parameter set and the slice header, and only coding a second syntax element in the slice header when both sets of deblocking filter parameters are present. Coding the second syntax element is eliminated when deblocking filter parameters are present in only one of the picture layer parameter set or the slice header. The second syntax element indicates which set of deblocking filter parameters to use to define a deblocking filter applied to a current slice.

This application claims the benefit of U.S. Provisional Application No.61/588,454, filed Jan. 19, 2012, U.S. Provisional Application No.61/593,015, filed Jan. 31, 2012, and U.S. Provisional Application No.61/620,339, filed Apr. 4, 2012, the entire content of each of which isincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video coding, and more particularly, todeblocking video data.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocompression techniques, such as those described in the standards definedby MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, AdvancedVideo Coding (AVC), the High Efficiency Video Coding (HEVC) standardpresently under development, and extensions of such standards. The videodevices may transmit, receive, encode, decode, and/or store digitalvideo information more efficiently by implementing such videocompression techniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (i.e., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to a referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modethat defines how the predictive block is created and the residual data.For further compression, the residual data may be transformed from thepixel domain to a transform domain, resulting in residual transformcoefficients, which then may be quantized. The quantized transformcoefficients, initially arranged in a two-dimensional array, may bescanned in order to produce a one-dimensional vector of transformcoefficients, and entropy coding may be applied to achieve even morecompression.

SUMMARY

In general, this disclosure describes techniques for signalingdeblocking filter parameters with reduced bitstream overhead for acurrent slice of video data. The deblocking filter parameters define adeblocking filter used to remove blockiness artifacts from decoded videoblocks of the slice. The deblocking filter parameters include syntaxelements defined to indicate whether deblocking filtering is enabled ordisabled and, if enabled, deblocking filter parameter offsets forthreshold values t_(c) and β. Deblocking filter parameters may be codedin one or more of a picture layer parameter set and a slice header. Thepicture layer parameter set may comprise either a picture parameter set(PPS) or an adaptation parameter set (APS).

The techniques may reduce a number of bits used to signal the deblockingfilter parameters by coding a first syntax element defined to indicatewhether deblocking filter parameters are present in both the picturelayer parameter set and the slice header, and only coding a secondsyntax element in the slice header when deblocking filter parameters arepresent in both the picture layer parameters set and the slice header.The second syntax element is defined to indicate whether to use a firstset of deblocking filter parameters included in the picture layerparameter set or a second set of deblocking filter parameters includedin the slice header to define the deblocking filter applied to thecurrent video slice. In this case, when deblocking filter parameters arepresent in only one of the picture layer parameter set or the sliceheader, a video encoder may eliminate encoding of the second syntaxelement in the slice header, and a video decoder may determine, based onthe first syntax element, that the second syntax element is not presentin the slice header to be decoded.

In one example, this disclosure is directed to a method of decodingvideo data, the method comprising decoding a first syntax elementdefined to indicate whether deblocking filter parameters are present inboth a picture layer parameter set and a slice header, when the firstsyntax element indicates that deblocking filter parameters are presentin both the picture layer parameter set and the slice header, decoding asecond syntax element in the slice header defined to indicate whether touse a first set of deblocking filter parameters included in the picturelayer parameter set or a second set of deblocking filter parametersincluded in the slice header to define a deblocking filter applied to acurrent video slice, and, when the first syntax element indicates thatdeblocking filter parameters are not present in both the picture layerparameter set and the slice header, determining that the second syntaxelement is not present in the slice header to be decoded.

In another example, this disclosure is directed to a video decodingdevice comprising a memory that stores video data, and a processorconfigured to decode a first syntax element defined to indicate whetherdeblocking filter parameters are present in both a picture layerparameter set and a slice header. The processor is configured to, whenthe first syntax element indicates that deblocking filter parameters arepresent in both the picture layer parameter set and the slice header,decode a second syntax element in the slice header defined to indicatewhether to use a first set of deblocking filter parameters included inthe picture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice. On the other hand, the processor isconfigured to, when the first syntax element indicates that deblockingfilter parameters are not present in both the picture layer parameterset and the slice header, determine that the second syntax element isnot present in the slice header to be decoded.

In a further example, this disclosure is directed to a video decodingdevice comprising means for decoding a first syntax element defined toindicate whether deblocking filter parameters are present in both apicture layer parameter set and a slice header, when the first syntaxelement indicates that deblocking filter parameters are present in boththe picture layer parameter set and the slice header, means for decodinga second syntax element in the slice header defined to indicate whetherto use a first set of deblocking filter parameters included in thepicture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice, and, when the first syntax elementindicates that deblocking filter parameters are not present in both thepicture layer parameter set and the slice header, means for determiningthat the second syntax element is not present in the slice header to bedecoded.

In another example, this disclosure is directed to a computer readablemedium comprising instructions for decoding video data that whenexecuted cause one or more processors to decode a first syntax elementdefined to indicate whether deblocking filter parameters are present inboth a picture layer parameter set and a slice header, when the firstsyntax element indicates that deblocking filter parameters are presentin both the picture layer parameter set and the slice header, decode asecond syntax element in the slice header defined to indicate whether touse a first set of deblocking filter parameters included in the picturelayer parameter set or a second set of deblocking filter parametersincluded in the slice header to define a deblocking filter applied to acurrent video slice, and, when the first syntax element indicates thatdeblocking filter parameters are not present in both the picture layerparameter set and the slice header, determine that the second syntaxelement is not present in the slice header to be decoded.

In an additional example, this disclosure is director to a method ofencoding video data, the method comprising encoding a first syntaxelement defined to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header, whenthe first syntax element indicates that deblocking filter parameters arepresent in both the picture layer parameter set and the slice header,encoding a second syntax element in the slice header defined to indicatewhether to use a first set of deblocking filter parameters included inthe picture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice, and, when the first syntax elementindicates that deblocking filter parameters are not present in both thepicture layer parameter set and the slice header, eliminating encodingof the second syntax element in the slice header.

In a further example, this disclosure is directed to a video encodingdevice comprising a memory that stores video data, and a processorconfigured to encode a first syntax element defined to indicate whetherdeblocking filter parameters are present in both a picture layerparameter set and a slice header. The processor is configured to, whenthe first syntax element indicates that deblocking filter parameters arepresent in both the picture layer parameter set and the slice header,encode a second syntax element in the slice header defined to indicatewhether to use a first set of deblocking filter parameters included inthe picture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice. On the other hand, the processor isconfigured to, when the first syntax element indicates that deblockingfilter parameters are not present in both the picture layer parameterset and the slice header, eliminate encoding of the second syntaxelement in the slice header.

In another example, this disclosure is directed to a video encodingdevice comprising means for encoding a first syntax element defined toindicate whether deblocking filter parameters are present in both apicture layer parameter set and a slice header, when the first syntaxelement indicates that deblocking filter parameters are present in boththe picture layer parameter set and the slice header, means for encodinga second syntax element in the slice header defined to indicate whetherto use a first set of deblocking filter parameters included in thepicture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice, and, when the first syntax elementindicates that deblocking filter parameters are not present in both thepicture layer parameter set and the slice header, means for eliminatingencoding of the second syntax element in the slice header.

In a further example, this disclosure is directed to a computer readablemedium comprising instructions for encoding video data that whenexecuted cause one or more processors to encode a first syntax elementdefined to indicate whether deblocking filter parameters are present inboth a picture layer parameter set and a slice header, when the firstsyntax element indicates that deblocking filter parameters are presentin both the picture layer parameter set and the slice header, encode asecond syntax element in the slice header defined to indicate whether touse a first set of deblocking filter parameters included in the picturelayer parameter set or a second set of deblocking filter parametersincluded in the slice header to define a deblocking filter applied to acurrent video slice, and, when the first syntax element indicates thatdeblocking filter parameters are not present in both the picture layerparameter set and the slice header, eliminate encoding of the secondsyntax element in the slice header.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may code deblocking filter parameters according tothe techniques described in this disclosure.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement the techniques described in this disclosure to encodedeblocking filter parameters with reduced bitstream overhead.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement the techniques described in this disclosure to decodedeblocking filter parameters used to define deblocking filters appliedto video slices.

FIG. 4 is a block diagram illustrating components of an exemplarydeblocking filter defined based on the deblocking filter parameterssignaled according to the techniques described in this disclosure.

FIG. 5 is a conceptual diagram illustrating pixel positions near an edgeof a video block between sub-blocks.

FIG. 6 is a flowchart illustrating an example operation of encodingdeblocking filter parameters for a current video slice with reducedbitstream overhead in accordance with the techniques described in thisdisclosure.

FIG. 7 is a flowchart illustrating an example operation of decodingdeblocking filter parameters for a current video slice with reducedbitstream overhead in accordance with the techniques described in thisdisclosure.

FIG. 8 is a flowchart illustrating an example operation of encodingdeblocking filter parameters for a current video slice in a pictureparameter set (PPS) that may be overridden by deblocking filterparameters in a slice header.

FIG. 9 is a flowchart illustrating an example operation of decodingdeblocking filter parameters for a current video slice in a pictureparameter set (PPS) that may be overridden by deblocking filterparameters in a slice header.

DETAILED DESCRIPTION

Some example techniques of this disclosure reduce the number of bitsused to signal deblocking filter parameters for a current video slice bycoding a first syntax element defined to indicate whether deblockingfilter parameters are present in both a picture layer parameter set anda slice header, and only coding a second syntax element in the sliceheader when deblocking filter parameters are present in both the picturelayer parameters set and the slice header. The second syntax element isdefined to indicate whether to use a first set of deblocking filterparameters included in the picture layer parameter set or a second setof deblocking filter parameters included in the slice header to definethe deblocking filter applied to the current video slice. In this case,when deblocking filter parameters are present in only one of the picturelayer parameter set or the slice header, a video encoding device mayeliminate encoding of the second syntax element in the slice header, anda video decoding device may determine, based on the first syntaxelement, that the second syntax element is not present in the sliceheader to be decoded.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may code deblocking filter parameters accordingto the techniques described in this disclosure. As shown in FIG. 1,system 10 includes a source device 12 that generates encoded video datato be decoded at a later time by a destination device 14. Source device12 and destination device 14 may comprise any of a wide range ofdevices, including desktop computers, notebook (i.e., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In some cases, source device 12 and destinationdevice 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia a link 16. Link 16 may comprise any type of medium or device capableof moving the encoded video data from source device 12 to destinationdevice 14. In one example, link 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In another example, link 16 may correspond to a storage medium that maystore the encoded video data generated by source device 12 and thatdestination device 14 may access as desired via disk access or cardaccess. The storage medium may include any of a variety of locallyaccessed data storage media such as Blu-ray discs, DVDs, CD-ROMs, flashmemory, or any other suitable digital storage media for storing encodedvideo data. In a further example, link 16 may correspond to a fileserver or another intermediate storage device that may hold the encodedvideo generated by source device 12 and that destination device 14 mayaccess as desired via streaming or download. The file server may be anytype of server capable of storing encoded video data and transmittingthat encoded video data to the destination device 14 Example fileservers include a web server (e.g., for a website), an FTP server,network attached storage (NAS) devices, or a local disk drive.Destination device 14 may access the encoded video data through anystandard data connection, including an Internet connection. This mayinclude a wireless channel (e.g., a Wi-Fi connection), a wiredconnection (e.g., DSL, cable modem, etc.), or a combination of both thatis suitable for accessing encoded video data stored on a file server.The transmission of encoded video data from the file server may be astreaming transmission, a download transmission, or a combination ofboth.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, streaming videotransmissions, e.g., via the Internet, encoding of digital video forstorage on a data storage medium, decoding of digital video stored on adata storage medium, or other applications. In some examples, system 10may be configured to support one-way or two-way video transmission tosupport applications such as video streaming, video playback, videobroadcasting, and/or video telephony.

In the example of FIG. 1, source device 12 includes a video source 18,video encoder 20 and an output interface 22. In some cases, outputinterface 22 may include a modulator/demodulator (modem) and/or atransmitter. In source device 12, video source 18 may include a sourcesuch as a video capture device, e.g., a video camera, a video archivecontaining previously captured video, a video feed interface to receivevideo from a video content provider, and/or a computer graphics systemfor generating computer graphics data as the source video, or acombination of such sources. As one example, if video source 18 is avideo camera, source device 12 and destination device 14 may formso-called camera phones or video phones. However, the techniquesdescribed in this disclosure may be applicable to video coding ingeneral, and may be applied to wireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby video encoder 20. The encoded video data may be transmitted directlyto destination device 14 via output interface 22 of source device 12.The encoded video data may also be stored onto a storage medium or afile server for later access by destination device 14 for decodingand/or playback.

Destination device 14 includes an input interface 28, a video decoder30, and a display device 32. In some cases, input interface 28 mayinclude a receiver and/or a modem. Input interface 28 of destinationdevice 14 receives the encoded video data over link 16. The encodedvideo data communicated over link 16, or provided on a data storagemedium, may include a variety of syntax elements generated by videoencoder 20 for use by a video decoder, such as video decoder 30, indecoding the video data. Such syntax elements may be included with theencoded video data transmitted on a communication medium, stored on astorage medium, or stored a file server.

Display device 32 may be integrated with, or external to, destinationdevice 14. In some examples, destination device 14 may include anintegrated display device and also be configured to interface with anexternal display device. In other examples, destination device 14 may bea display device. In general, display device 32 displays the decodedvideo data to a user, and may comprise any of a variety of displaydevices such as a liquid crystal display (LCD), a plasma display, anorganic light emitting diode (OLED) display, or another type of displaydevice.

Video encoder 20 and video decoder 30 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video compressionstandards include MPEG-2 and ITU-T H.263.

Although not shown in FIG. 1, in some aspects, video encoder 20 andvideo decoder 30 may each be integrated with an audio encoder anddecoder, and may include appropriate MUX-DEMUX units, or other hardwareand software, to handle encoding of both audio and video in a commondata stream or separate data streams. If applicable, in some examples,MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, orother protocols such as the user datagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

The Joint Collaborative Team on Video Coding (JCT-VC) is working ondevelopment of the HEVC standard. The HEVC standardization efforts arebased on an evolving model of a video coding device referred to as theHEVC Test Model (HM). The HM presumes several additional capabilities ofvideo coding devices relative to existing devices according to, e.g.,ITU-T H.264/AVC. For example, whereas H.264 provides nineintra-prediction encoding modes, the HM may provide as many asthirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. A treeblock has asimilar purpose as a macroblock of the H.264 standard. A slice includesa number of consecutive treeblocks in coding order. A video frame orpicture may be partitioned into one or more slices. Each treeblock maybe split into coding units (CUs) according to a quadtree. For example, atreeblock, as a root node of the quadtree, may be split into four childnodes, and each child node may in turn be a parent node and be splitinto another four child nodes. A final, unsplit child node, as a leafnode of the quadtree, comprises a coding node, i.e., a coded videoblock. Syntax data associated with a coded bitstream may define amaximum number of times a treeblock may be split, and may also define aminimum size of the coding nodes.

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node. The size of the CU may rangefrom 8×8 pixels up to the size of the treeblock with a maximum of 64×64pixels or greater. Each CU may contain one or more PUs and one or moreTUs. Syntax data associated with a CU may describe, for example,partitioning of the CU into one or more PUs. Partitioning modes maydiffer between whether the CU is skip or direct mode encoded,intra-prediction mode encoded, or inter-prediction mode encoded. PUs maybe partitioned to be square or non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU may be partitionedto be square or non-square in shape.

In general, a PU includes data related to the prediction process. Forexample, when the PU is intra-mode encoded, the PU may include datadescribing an intra-prediction mode for the PU. As another example, whenthe PU is inter-mode encoded, the PU may include data defining a motionvector for the PU. The data defining the motion vector for a PU maydescribe, for example, a horizontal component of the motion vector, avertical component of the motion vector, a resolution for the motionvector (e.g., one-quarter pixel precision or one-eighth pixelprecision), a reference picture to which the motion vector points,and/or a reference picture list (e.g., List 0 or List 1) for the motionvector.

In general, a TU is used for the transform and quantization processes. ACU having one or more PUs may also include one or more TUs. Followingprediction, video encoder 20 may calculate residual values correspondingto the PU. The residual values comprise pixel difference values that maybe transformed into transform coefficients, quantized, and scanned usingthe TUs to produce serialized transform coefficients for entropy coding.This disclosure typically uses the term “video block” to refer to acoding node of a CU. In some specific cases, this disclosure may alsouse the term “video block” to refer to a treeblock, i.e., LCU, or a CU,which includes a coding node and PUs and TUs.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up”, “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N'0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs including the residual data for the CU, and thentransform the TUs to produce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the coefficients.

In some examples, video encoder 20 may utilize a predefined scan orderto scan the quantized transform coefficients to produce a serializedvector that can be entropy encoded. In other examples, video encoder 20may perform an adaptive scan. After scanning the quantized transformcoefficients to form a one-dimensional vector, video encoder 20 mayentropy encode the one-dimensional vector, e.g., according to contextadaptive variable length coding (CAVLC), context adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), probability interval partitioning entropycodes (PIPE), or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

In addition to signaling the encoded video data in a bitstream to videodecoder 30 in destination device 14, video encoder 20 may also decodethe encoded video data and reconstruct the blocks within a video frameor picture for use as reference data during the intra- orinter-prediction process for subsequently coded blocks. After dividing avideo frame or picture into blocks (e.g., LCUs and sub-CUs thereof),encoding the blocks, and then decoding the blocks, however, perceptibleartifacts at edges between the blocks may occur. In order to removethese “blockiness” artifacts, video encoder 20 may apply deblockingfilters to the decoded video blocks prior to storage as referenceblocks. Similarly, video decoder 30 may be configured to decode videodata received in a bitstream from video encoder 20 of source device 12,and apply the same or similar deblocking filters to the decoded videodata for purposes of displaying the video data as well as for using thevideo data as reference data for subsequently decoded video data.

Deblocking filtering performed by a video coding device, such as a videoencoder 20 or video decoder 30, prior to storing the data for use asreference data is generally referred to as “in-loop” filtering, in thatthe filtering is performed within the coding loop. By configuring bothvideo encoder 20 and video decoder 30 to apply the same deblockingtechniques, the video coding devices can be synchronized, such thatdeblocking does not introduce error for subsequently coded video datathat uses the deblocked video data as reference data.

Video encoder 20 and video decoder 30 are generally configured todetermine, for each edge of a video block, including PU and TU edges,whether to apply a deblocking filter to deblock the edge. The videocoding devices may be configured to determine whether to deblock an edgebased on an analysis of one or more lines of pixels perpendicular to theedge, e.g., a line of 8 pixels. Thus, for example, for a vertical edge,a video coding device may determine whether to deblock the edge byexamining four pixels to the left and four pixels to the right of theedge along a common line. The number of pixels selected generallycorresponds to the smallest block for deblocking, e.g., 8×8 pixels. Inthis manner, the line of pixels used for analysis stretches across PUand TU edges of the video block with pixels on either side of the edge,e.g., to the left and right of an edge or above and below an edge. Theline of pixels used for analysis of whether to perform deblocking for anedge is also referred to as a set of support pixels, or simply“support.”

Video coding devices may be configured to execute deblocking decisionfunctions based on the support for a particular edge. In general,deblocking decision functions are configured to detect high-frequencychanges within the support pixels. Typically, when a high frequencychange is detected, the deblocking decision function provides anindication that perceptible artifacts are present at the edge anddeblocking should occur. The deblocking decision functions may also beconfigured to determine a type and strength of the deblocking filter toapply to the edge based on the support. The type and strength of thedeblocking filter may be indicated by threshold values t_(c) and β.

This disclosure describes techniques for signaling deblocking filterparameters for a current slice of video data with reduced bitstreamoverhead. The deblocking filter parameters define a deblocking filterused to reduce or remove blockiness artifacts from decoded video blocksof the current slice. The deblocking filter parameters include syntaxelements configured to indicate whether deblocking filtering is enabledor disabled and, if enabled, deblocking filter parameter offsets forthreshold values t_(c) and β.

Deblocking filter parameters may be coded in one or more of a picturelayer parameter set and a slice header. The picture layer parameter setmay comprise either a picture parameter set (PPS) or an adaptationparameter set (APS). The PPS is a picture layer parameter set thatcontains data unlikely to change between pictures that refer to the PPS.The APS is a picture layer parameter set intended for use withpicture-adaptive data that is likely to change from picture to picture.In one example, the APS includes parameters for a deblocking filter, anAdaptive Loop Filter (ALF), and a Sample Adaptive Offset (SAO).Including these parameters in the APS instead of the PPS may reduce anumber of bits transmitted for a video sequence because constant PPSdata does not need to be repeated when the deblocking filter, ALF, orSAO parameters change.

FIG. 2 is a block diagram illustrating an example of video encoder 20that may implement the techniques described in this disclosure to encodedeblocking filter parameters with reduced bitstream overhead. Videoencoder 20 may perform intra- and inter-coding of video blocks withinvideo slices. Intra-coding relies on spatial prediction to reduce orremove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased compression modes. Inter-modes, such as uni-directional prediction(P mode) or bi-prediction (B mode), may refer to any of severaltemporal-based compression modes.

In the example of FIG. 2, video encoder 20 includes mode select unit 40,motion estimation unit 42, motion compensation unit 44, intra predictionprocessing unit 46, reference picture memory 64, summer 50, transformprocessing unit 52, quantization unit 54, and entropy encoding unit 56.For video block reconstruction, video encoder 20 also includes inversequantization unit 58, inverse transform processing unit 60, and summer62. A deblocking filter 63 is also included to filter block boundariesto remove blockiness artifacts from reconstructed video blocks.

As shown in FIG. 2, video encoder 20 receives a current video blockwithin a video slice to be encoded. The slice may be divided intomultiple video blocks. Mode select unit 40 may select one of the codingmodes, intra or inter, for the current video block based on errorresults. If the intra or inter modes are selected, mode selection unit40 provides the resulting intra- or inter-coded block to summer 50 togenerate residual block data and to summer 62 to reconstruct the encodedblock for use as a reference block within a reference picture stored inreference picture memory 64. Intra prediction processing unit 46performs intra-predictive coding of the current video block relative toone or more neighboring blocks in the same frame or slice as the currentblock to be coded to provide spatial compression. Motion estimation unit42 and motion compensation unit 44 perform inter-predictive coding ofthe current video block relative to one or more predictive blocks in oneor more reference pictures to provide temporal compression.

In the case of inter-coding, motion estimation unit 42 may be configuredto determine the inter-prediction mode for a video slice according to apredetermined pattern for a video sequence. The predetermined patternmay designate video slices in the sequence as P slices or B slices.Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference picture.

A predictive block is a block that is found to closely match the PU ofthe video block to be coded in terms of pixel difference, which may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. In some examples, video encoder 20may calculate values for sub-integer pixel positions of referencepictures stored in reference picture memory 64. For example, videoencoder 20 may calculate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference picture memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation. Upon receiving the motion vectorfor the PU of the current video block, motion compensation unit 44 maylocate the predictive block to which the motion vector points in one ofthe reference picture lists. Video encoder 20 forms a residual videoblock by subtracting pixel values of the predictive block from the pixelvalues of the current video block being coded, forming pixel differencevalues. The pixel difference values form residual data for the block,and may include both luma and chroma difference components. Summer 50represents the component or components that perform this subtractionoperation. Motion compensation unit 44 may also generate syntax elementsassociated with the video blocks and the video slice for use by videodecoder 30 in decoding the video blocks of the video slice.

After motion compensation unit 44 generates the predictive block for thecurrent video block, video encoder 20 forms a residual video block bysubtracting the predictive block from the current video block. Theresidual video data in the residual block may be included in one or moreTUs and applied to transform processing unit 52. Transform processingunit 52 transforms the residual video data into residual transformcoefficients using a transform, such as a discrete cosine transform(DCT) or a conceptually similar transform. Transform processing unit 52may convert the residual video data from a pixel domain to a transformdomain, such as a frequency domain.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of the matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), or another entropy encodingtechnique. Following the entropy encoding by entropy encoding unit 56,the encoded bitstream may be transmitted to video decoder 30, orarchived for later transmission or retrieval by video decoder 30.Entropy encoding unit 56 may also entropy encode the motion vectors andthe other syntax elements for the current video slice being coded.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual block in the pixel domain for later use as areference block of a reference picture. Motion compensation unit 44 maycalculate a reference block by adding the residual block to a predictiveblock of one of the reference pictures within one of the referencepicture lists. Motion compensation unit 44 may also apply one or moreinterpolation filters to the reconstructed residual block to calculatesub-integer pixel values for use in motion estimation. Summer 62 addsthe reconstructed residual block to the motion compensated predictionblock produced by motion compensation unit 44 to produce a referenceblock of a reference picture for storage in reference picture memory 64.The reference block is filtered by deblocking filter 63 in order toremove blockiness artifacts. The reference block is then stored inreference picture memory 64. The reference block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-predict a block in a subsequent video frame or picture.

In accordance with the techniques of this disclosure, video encoder 20includes deblocking filter 63 that selectively filters the output ofsummer 62. In particular, deblocking filter 63 receives reconstructedvideo data from summer 62, which corresponds to predictive data receivedfrom either motion compensation unit 44 or intra-prediction unit 46added to inverse quantized and inverse transformed residual data. Inthis manner, deblocking filter 63 receives decoded blocks of video data,e.g., decoded blocks corresponding to CUs of an LCU and/or LCUs of aslice or picture, and selectively filters the blocks to removeblockiness artifacts.

Deblocking filter 63 in video encoder 20 filters certain TU and PU edgesof a decoded video block based on a result from a boundary strengthcomputation and deblocking decisions. Deblocking filter 63 is generallyconfigured to analyze pixels of a video block near a given edge of theblock to determine whether and how to deblock the edge. Moreparticularly, the deblocking decisions may include whether thedeblocking filter is on or off, whether the deblocking filter is weak orstrong, and the strength of the weak filter for a given video block.Deblocking filter 63 may alter the values of the pixels near the givenedge when a high-frequency change in values is detected in order toremove blockiness artifacts perceptible at the edge.

The boundary strength computation and the deblocking decisions aredependent on threshold values t_(c) and β. The threshold values t_(c)and β of the deblocking filter depend on a parameter Q, which is derivedfrom a quantization parameter (QP) value and a boundary strength (Bs)for the current video block as follows:

If Bs=2,then TcOffset=2

If Bs≦1,then TcOffset=0

For t _(C) : Q=Clip3(0,MAX_QP+2,QP+TcOffset);MAX_QP=51

For β: Q=Clip3(0,MAX_QP,QP)

Clip3(th1,th2,value)=min(th1,max(th2,value))

The threshold values t_(c) and β may be stored in a table that isaccessible based on the parameter Q derived from the QP value of thevideo block. The deblocking process is described in more detail belowwith respect to deblocking filter 100 illustrated in FIG. 4.

This disclosure describes techniques for signaling, with reducedbitstream overhead, deblocking filter parameters used to definedeblocking filter 63 for a current slice of video data. Video encoder 20determines the deblocking filter parameters that define deblockingfilter 63 and then signals the deblocking filter parameters so thatvideo decoder 30 can apply the same or similar deblocking filter todecoded video blocks. The deblocking filter parameters include syntaxelements defined to indicate whether deblocking filtering is enabled ordisabled and, if enabled, deblocking filter parameter offsets forthreshold values t_(c) and β.

Deblocking filter parameters may be coded in one or more of a picturelayer parameter set and a slice header for signaling to video decoder30. The picture layer parameter set may comprise either a pictureparameter set (PPS) or an adaptation parameter set (APS). The PPS is apicture layer parameter set that contains data unlikely to changebetween pictures that refer to the PPS. The APS is a picture layerparameter set intended for use with picture-adaptive data that is likelyto change from picture to picture.

Entropy encoding unit 56 of video encoder 20 encodes a first syntaxelement defined to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header forpictures referring to the picture layer parameter set. According to thetechniques described in this invention, entropy encoding unit 56 encodesdeblocking filter parameters for a current video slice with reducedbitstream overhead by only encoding a second syntax element in the sliceheader when deblocking filter parameters are present in both the picturelayer parameter set and the slice header.

When deblocking filter parameters are not present in both the picturelayer parameter set and the slice header, entropy encoding unit 56eliminates coding a second syntax element in the slice header defined toindicate which set of deblocking filter parameters is used to definedeblocking filter 63 for a current video slice. In the case wheredeblocking filter parameters are only present in one of the picturelayer parameter set or the slice header, deblocking filter 63 is definedfor the current video slice based on the set of deblocking filterparameters that are present in either the picture layer parameter set orthe slice header. The second syntax element, therefore, is unnecessaryto indicate the deblocking filter parameters to video decoder 30 becauseno decision needs to made between the picture layer parameter set andthe slice header regarding which set of deblocking filter parameters touse to define the deblocking filter at video decoder 30.

When the deblocking filter parameters are present in both the picturelayer parameter set and the slice header, entropy encoding unit 56encodes the second syntax element in the slice header defined toindicate whether to use a first set of deblocking parameters included inthe picture layer parameter set or a second set of deblocking parametersincluded in the slice header. In this case, deblocking filter 63 isdefined for the current video slice based on one of the first set or thesecond set of deblocking parameters. The second syntax element,therefore, is necessary to indicate the deblocking filter parametersused to define deblocking filter 63 in video encoder 20 so that videodecoder 30 can apply the same or similar deblocking filter to decodedvideo blocks.

In some cases, entropy encoding unit 56 may also encode a controlpresent syntax element defined to indicate whether any deblocking filtercontrol syntax elements are present in either the picture layerparameter set or the slice header. The control present syntax elementmay be signaled in the picture layer parameter set or from ahigher-layer parameter set, e.g., a sequence parameter set (SPS). Thedeblocking filter control syntax elements comprise the first and secondsyntax elements described above. Entropy encoding unit 56, therefore,encodes the control present syntax element prior to encoding the firstsyntax element. If no deblocking filter control syntax elements arepresent, video encoder 20 notifies video decoder 30 and does not encodethe first or second syntax elements. In this case, video encoder 20 mayuse default deblocking filter parameters to define deblocking filter 63applied to the decoded video blocks.

In other cases, entropy encoding unit 56 may encode a deblocking filterenabled syntax element defined to indicate whether deblocking filter 63is enabled for one or more pictures of a video sequence prior toencoding the first syntax element. The deblocking filter enabled syntaxelement may be signaled in a higher-layer parameter set, e.g., asequence parameter set (SPS). If deblocking filter 63 is disabled forthe video sequence, video encoder 20 notifies video decoder 30 and doesnot encode the first or second syntax elements because deblocking filter63 is not applied to the decoded video blocks. In this case, videoencoder 20 also does not encode a control present syntax element.

In one example, the first syntax element comprises an override enabledflag coded in a PPS for a given picture. In this case, a first set ofdeblocking filter parameters is coded in the PPS and the overrideenabled flag indicates whether a second set of deblocking filterparameters is present in a slice header for one or more slices of thegiven picture that could be used to override the parameters from thePPS. In addition, the second syntax element comprises an override flagthat may be coded in the slice header. When the override enabled flag inthe PPS indicates that the second set of deblocking filter parameters ispresent in the slice header, entropy encoding unit 56 encodes theoverride flag to indicate to video decoder 30 whether to use the firstset of deblocking filter parameters in the PPS or to override the firstset of deblocking filter parameters with the second set of deblockingfilter parameters included in the slice header to define the deblockingfilter at video decoder 30. Otherwise, when the override enabled flag inthe PPS indicates that only the first set of deblocking filterparameters in the PPS is present, entropy encoding unit 56 eliminatesencoding of the override flag in the slice header. The specific syntaxelements for this example are described in more detail below withrespect to video decoder 30 in FIG. 3.

In another example, the first syntax element comprises an inheritenabled flag coded in a SPS and/or an APS for a given picture. In thiscase, a second set of deblocking filter parameters is coded in the sliceheader and the inherit enabled flag indicates whether a first set ofdeblocking filter parameters is present in the APS that could beinherited by the slice header. The second syntax element comprises aninherit flag that may be coded in the slice header. When the inheritenabled flag in the SPS and/or APS indicates that the first set ofdeblocking filter parameters is present in the APS, entropy encodingunit 56 encodes the inherit flag to indicate to video decoder 30 whetherto use the second set of deblocking filter parameters in the sliceheader or to inherit the first set of deblocking filter parameters inthe APS to define the deblocking filter at video decoder 30. Otherwise,when the inherit enabled flag in the SPS and/or APS indicates that onlythe second set of deblocking filter parameters in the slice header ispresent, entropy encoding unit 56 eliminates encoding of the inheritflag in the slice header. The specific syntax elements for this exampleare described in more detail below with respect to video decoder 30 inFIG. 3.

FIG. 3 is a block diagram illustrating an example of a video decoder 30that may implement the techniques described in this disclosure to decodedeblocking filter parameters used to define deblocking filters appliedto video slices. In the example of FIG. 3, video decoder 30 includes anentropy decoding unit 80, a prediction processing unit 81, an inversequantization unit 86, an inverse transform processing unit 88, a summer90, a deblocking filter 91, and a reference picture memory 92.Prediction processing unit 81 includes motion compensation unit 82 andintra prediction processing unit 84. Video decoder 30 may, in someexamples, perform a decoding pass generally reciprocal to the encodingpass described with respect to video encoder 20 from FIG. 2.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. When the representedvideo blocks in the bitstream include compressed video data, entropydecoding unit 80 of video decoder 30 entropy decodes the bitstream togenerate quantized coefficients, motion vectors, and other syntaxelements. Entropy decoding unit 80 forwards the motion vectors and othersyntax elements to prediction processing unit 81. Video decoder 30 mayreceive the syntax elements at a sequence level, a picture level, aslice level and/or a video block level. In some cases, entropy decodingunit 80 decodes deblocking filter control syntax elements, includingdeblocking filter parameters, to define a deblocking filter 91 for agiven video slice.

When the video slice is coded as an intra-coded (I) slice, intraprediction processing unit 84 of prediction processing unit 81 maygenerate prediction data for a video block of the current video slicebased on a signaled intra prediction mode and data from previouslydecoded blocks of the current frame or picture. When the video frame iscoded as an inter-coded (i.e., B or P) slice, motion compensation unit82 of prediction processing unit 81 produces predictive blocks for avideo block of the current video slice based on the motion vectors andother syntax elements received from entropy decoding unit 80. Thepredictive blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference frame lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in referencepicture memory 92.

Motion compensation unit 82 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 82 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice or P slice), constructioninformation for one or more of the reference picture lists for theslice, motion vectors for each inter-encoded video block of the slice,inter-prediction status for each inter-coded video block of the slice,and other information to decode the video blocks in the current videoslice.

Motion compensation unit 82 may also perform interpolation based oninterpolation filters. Motion compensation unit 82 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. Motion compensation unit 82 may determine the interpolationfilters used by video encoder 20 from the received syntax elements anduse the interpolation filters to produce predictive blocks.

Inverse quantization unit 86 inverse quantizes, i.e., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter calculated by video encoder 20for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied. Inverse transform processing unit 88 applies an inversetransform, e.g., an inverse DCT, an inverse integer transform, or aconceptually similar inverse transform process, to the transformcoefficients in order to produce residual blocks in the pixel domain.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform processing unit 88 with thecorresponding predictive blocks generated by motion compensation unit82. Summer 90 represents the component or components that perform thissummation operation. A deblocking filter 91 is applied to filter theblocks received from summer 90 in order to remove blockiness artifacts.The decoded video blocks in a given picture are then stored in referencepicture memory 92, which stores reference pictures used for subsequentmotion compensation. Reference picture memory 92 also stores decodedvideo for later presentation on a display device, such as display device32 of FIG. 1.

Deblocking filter 91 in video decoder 30 filters certain TU and PU edgesof a decoded video block based on a result from a boundary strengthcomputation and deblocking decisions. The boundary strength computationand the deblocking decisions are dependent on threshold values t_(c) andβ, which may be signaled to video decoder 30 from video encoder 20 usingsyntax elements. Deblocking filter 91 may alter the values of pixelsnear a given edge of a video block in order to remove blockinessartifacts perceptible at the edge. Deblocking filter 91 conformssubstantially to deblocking filter 63 from FIG. 2 in that deblockingfilter 91 may be configured to perform any or all of the techniquesdescribed with respect to deblocking filter 63. The deblocking processis described in more detail below with respect to deblocking filter 100illustrated in FIG. 4.

In accordance with the techniques of this disclosure, entropy decodingunit 80 in video decoder 30 decodes deblocking filter control syntaxelements included in the bitstream received from video encoder 20. Thedeblocking filter control syntax elements include deblocking filterparameters that indicate whether deblocking filtering is enabled ordisabled and, if enabled, deblocking filter parameter offsets forthreshold values t_(c) and β. Video encoder 30 determines the deblockingfilter parameters to be used for deblocking filter 91 from thedeblocking filter control syntax elements included in the bitstream.Video decoder 30 then defines deblocking filter 91 based on thedeblocking filter parameters to operate the same or similar todeblocking filter 63 in video encoder 20 in order to decode the videoblocks in the bitstream.

This disclosure describes techniques for signaling, with reducedbitstream overhead, deblocking filter parameters used to definedeblocking filter 91 for a current slice of video data. Deblockingfilter parameters may be coded in one or more of a picture layerparameter set and a slice header for signaling to video decoder 30. Thepicture layer parameter set may comprise either a picture parameter set(PPS) or an adaptation parameter set (APS). The PPS is a picture layerparameter set that contains data unlikely to change between picturesthat refer to the PPS. The APS is a picture layer parameter set intendedfor use with picture-adaptive data that is likely to change from pictureto picture.

Entropy decoding unit 80 of video encoder 30 decodes a first syntaxelement defined to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header forpictures referring to the picture layer parameter set. According to thetechniques described in this invention, entropy decoding unit 80 onlydecodes a second syntax element in the slice header when deblockingfilter parameters are present in both the picture layer parameter setand the slice header.

When deblocking filter parameters are not present in both the picturelayer parameter set and the slice header, entropy decoding unit 80determines that a second syntax element defined to indicate which set ofdeblocking filter parameters to use to define deblocking filter 91 for acurrent video slice is not present in the slice header to be decoded. Inthe case where deblocking filter parameters are only present in one ofthe picture layer parameter set or the slice header, deblocking filter91 is defined for the current video slice based on the set of deblockingfilter parameters that are present in either the picture layer parameterset or the slice header. The second syntax element, therefore, isunnecessary because video decoder 30 does not need to decide which setof deblocking filter parameters to use to define deblocking filter 91 invideo decoder 30.

When the deblocking filter parameters are present in both the picturelayer parameter set and the slice header, entropy decoding unit 80decodes the second syntax element in the slice header defined toindicate whether to use a first set of deblocking parameters included inthe picture layer parameter set or a second set of deblocking parametersincluded in the slice header. In this case, deblocking filter 91 isdefined for the current video slice based on one of the first set or thesecond set of deblocking parameters. The second syntax element,therefore, is necessary so that video decoder 30 knows which set ofdeblocking filter parameters to use to define deblocking filter 91 to bethe same or similar to deblocking filter 63 in video encoder 20.

In some cases, entropy decoding unit 80 may also decode a controlpresent syntax element defined to indicate whether any deblocking filtercontrol syntax elements are present in either the picture layerparameter set or the slice header. The control present syntax elementmay be decoded from the picture layer parameter set or from ahigher-layer parameter set, e.g., a sequence parameter set (SPS). Thedeblocking filter control syntax elements comprise the first and secondsyntax elements described above. Entropy decoding unit 80, therefore,decodes the control present syntax element prior to decoding the firstsyntax element. If the control present syntax element indicates that nodeblocking filter control syntax elements are present, video decoder 30knows that it does not need to decode the first or second syntaxelements because the first and second syntax elements are not present inthe bitstream to be decoded. In this case, video decoder 30 may usedefault deblocking filter parameters to define deblocking filter 91applied to the decoded video blocks.

In other cases, entropy decoding unit 80 may decode a deblocking filterenabled syntax element defined to indicate whether deblocking filter 91is enabled for one or more pictures of a video sequence prior todecoding the first syntax element. The deblocking filter enabled syntaxelement may be decoded from a higher-layer parameter set, e.g., asequence parameter set (SPS). If deblocking filter 91 is disabled forthe video sequence, video decoder 30 knows that it does not need todecode the first or second syntax elements because deblocking filter 91is not applied to the decoded video blocks. In this case, video decoder30 also does not need to decode a control present syntax element.

In one example, the first syntax element comprises an override enabledflag coded in a PPS for a given picture. In this case, a first set ofdeblocking filter parameters is coded in the PPS and the overrideenabled flag indicates whether a second set of deblocking filterparameters is present in a slice header for one or more slices of thegiven picture that could be used to override the parameters from thePPS. In addition, the second syntax element comprises an override flagthat may be coded in the slice header. When the override enabled flag inthe PPS indicates that the second set of deblocking filter parameters ispresent in the slice header, entropy decoding unit 80 decodes theoverride flag to determine whether to use the first set of deblockingfilter parameters in the PPS or to override the first set of deblockingfilter parameters with the second set of deblocking filter parametersincluded in the slice header to define deblocking filter 91. Otherwise,when the override enabled flag in the PPS indicates that only the firstset of deblocking filter parameters in the PPS is present, entropydecoding unit 80 determines that the override flag is not present in theslice header to be decoded.

Table 1 provides an exemplary portion of the PPS syntax including anoverride enabled flag, i.e., deblocking_filter_override_enabled_flag,and a control present syntax element, i.e.,deblocking_filter_control_present_flag.

TABLE 1 PPS Syntax with override enabled flag pic_parameter_set_rbsp( ){ Descriptor . . .  deblocking_filter_control_present_flag u(1)  if(deblocking_filter_control_present_flag ) {  deblocking_filter_override_enabled_flag u(1)  pic_disable_deblocking_filter_flag u(1)   if(!pic_disable_deblocking_filter_flag ) {    beta_offset_div2 se(v)   tc_offset_div2 se(v)   }  } . . .

Semantics for the PPS syntax of Table 1 are defined as follows. Thedeblocking_filter_control_present_flag equal to 1 specifies the presenceof deblocking filter control syntax elements in the picture parameterset and in the slice header for pictures referring to the pictureparameter set. The deblocking_filter_control_present_flag equal to 0specifies the absence of deblocking filter control syntax elements inthe picture parameter set and in the slice header for pictures referringto the picture parameter set.

The deblocking_filter_override_enabled_flag equal to 1 specifies thepresence of a deblocking_filter_override_flag in the slice header forpictures referring to the picture parameter set. Thedeblocking_filter_override_enabled_flag equal to 0 specifies the absenceof the deblocking_filter_override_flag in the slice header for picturesreferring to the picture parameter set. When not present, the value ofthe deblocking_filter_override_enabled_flag is inferred to be equal to0.

The pic_disable_deblocking_filter_flag equal to 1 specifies that theoperation of the deblocking filter shall not be applied for picturesreferring to the picture parameter set whendeblocking_filter_override_enabled_flag is equal to 0. Thepic_disable_deblocking_filter_flag equal to 0 specifies that theoperation of the deblocking filter shall be applied for picturesreferring to the picture parameter set when thedeblocking_filter_override_enabled_flag is equal to 0. When not present,the value of the pic_disable_deblocking_filter_flag is inferred to beequal to 0.

The beta_offset_div2 and tc_offset_div2 syntax elements specify thedefault deblocking parameter offsets for β and t_(c) (divided by 2) thatare applied for pictures referring to the picture parameter set unlessthe default deblocking parameter offsets are overridden by thedeblocking parameter offsets present in the slice segment header forpictures referring to the picture parameter set. The values of thebeta_offset_div2 and tc_offset_div2 syntax elements shall both be in therange of −6 to 6, inclusive. When not present, the value of thebeta_offset_div2 and tc_offset_div2 syntax elements is inferred to beequal to 0.

Table 2 provides an exemplary portion of the slice header syntaxincluding an override flag, i.e., deblocking_filter_override_flag, thatis conditionally coded based on the override enabled flag and thecontrol present syntax element in the PPS syntax.

TABLE 2 Slice Header Syntax with override flag slice_segment_header( ) {Descriptor . . .  if( deblocking_filter_control_present_flag ) {   if(deblocking_filter_override_enabled_flag )   deblocking_filter_override_flag u(1)   if(deblocking_filter_override_flag ) {   slice_disable_deblocking_filter_flag u(1)    if(!slice_disable_deblocking_filter_flag ) {     beta_offset_div2 se(v)    tc_offset_div2 se(v)    }   }  } . . .

Semantics for the slice header syntax of Table 2 are defined as follows.The deblocking_filter_override_flag equal to 0 specifies that deblockingparameters from the active picture parameter set are used for deblockingthe current slice. The deblocking_filter_override_flag equal to 1specifies that deblocking parameters from the slice segment header areused for deblocking the current slice. When not present, the value ofthe deblocking_filter_override_flag is inferred to be equal to 0.

The slice_disable_deblocking_filter_flag equal to 1 specifies that theoperation of the deblocking filter is not applied for the current slice.The slice_disable_deblocking_filter_flag equal to 0 specifies that theoperation of the deblocking filter is applied for the current slice.When the slice_disable_deblocking_filter_flag is not present, it isinferred to be equal to the pic_disable_deblocking_filter_flag in thePPS syntax.

The beta_offset_div2 and tc_offset_div2 syntax elements specify thedeblocking parameter offsets for β and t_(c) (divided by 2) for thecurrent slice. The values of the beta_offset_div2 and tc_offset_div2syntax elements shall be in the range of −6 to 6, inclusive.

In another example, the first syntax element comprises an inheritenabled flag coded in a SPS and/or an APS for a given picture. In thiscase, a second set of deblocking filter parameters is coded in the sliceheader and the inherit enabled flag indicates whether a first set ofdeblocking filter parameters is present in the APS that could beinherited by the slice header. The second syntax element comprises aninherit flag that may be coded in the slice header. When the inheritenabled flag in the SPS and/or the APS indicates that the first set ofdeblocking filter parameters is present in the APS, entropy decodingunit 80 decodes the inherit flag to determine whether to use the secondset of deblocking filter parameters in the slice header or to inheritthe first set of deblocking filter parameters in the APS to definedeblocking filter 91. Otherwise, when the inherit enabled flag in theSPS and/or the APS indicates that only the second set of deblockingfilter parameters in the slice header is present, entropy decoding unit80 determines that the inherit flag is not present in the slice headerto be decoded.

Signaling deblocking filter parameters to a video decoder was proposedin A. Norkin, “BoG report on resolving deblocking filter descriptionissues,” 7^(th) JCT-VC Meeting, Geneva, CH, November 2011, Doc. JCT-VCG1035_r1+update. Table 3 provides an example of the SPS syntax includingan inherit enabled flag, i.e., deblocking_filter_in_aps_enabled_flag.

TABLE 3 SPS syntax with inherit enabled flag seq_parameter_set_rbsp( ) {Descriptor  profile_idc u(8)  (omitted) chroma_pred_from_luma_enabled_flag u(1) deblocking_filter_in_aps_enabled_flag u(1) loop_filter_across_slice_flag u(1)  sample_adaptive_offset_enabled_flagu(1)  adaptive_loop_filter_enabled_flag u(1) pcm_loop_filter_disable_flag u(1)  cu_qp_delta_enabled_flag u(1) temporal_id_nesting_flag u(1)  inter_4x4_enabled_flag u(1) rbsp_trailing_bits( ) }

Table 4 provides an example of the APS syntax including an inheritenabled flag, i.e., aps_deblocking_filter_flag.

TABLE 4 APS syntax with inherit enabled flag aps_rbsp( ) { Descriptor aps_id ue(v)  aps_deblocking_filter_flag u(1) aps_sample_adaptive_offset_flag u(1)  aps_adaptive_loop_filter_flagu(1)  if( aps_sample_adaptive_offset_flag || aps_adaptive_loop_filter_flag ) {   aps_cabac_use_flag u(1)   if(aps_cabac_use_flag ) {    aps_cabac_init_idc ue(v)   aps_cabac_init_qp_minus26 se(v)   }  }  if(aps_deblocking_filter_flag){   disable_deblocking_filter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_ offset_div2 se(v)   tc_offset_div2 se(v)   }  }  if( aps_sample_adaptive_offset_flag ) {  sao_data_byte_count u(8)   byte_align( )   sao_param( )   byte_align()  }  if( aps_adaptive_loop_filter_flag ) {   alf_data_byte_count u(8)  byte_align( )   alf_param( )  }  rbsp_trailing_bits( ) }

Semantics for the SPS and APS syntax of Tables 3 and 4 are defined asfollows. The deblocking_filter_in_aps_enabled_flag in the SPS equal to 0means deblocking filter parameters are present in the slice header, andequal to 1 means deblocking filter parameters are present in the APS.The aps_deblocking_filter_flag in the APS is equal to thedeblocking_filter_in_aps_enabled_flag in the SPS. Theaps_deblocking_filter_flag indicates that deblocking filter parametersare present in the APS (equal to 1) or not present in the APS (equal to0).

One issue with the signaling of deblocking filter parameters is that theinherit flag is signaled in the slice header even when deblocking filterparameters are not present in the APS. As described above, whendeblocking filter parameters are only present in the slice header andnot present in the APS, the deblocking filter is defined based on thepresent deblocking filter parameters in the slice header and the inheritflag is unnecessary. Table 5 provides an exemplary portion of the sliceheader syntax including an inherit flag, i.e.,inherit_dbl_params_from_APS_flag, that is conditionally coded based onthe inherit enabled flags in the APS syntax and the SPS syntax.

TABLE 5 Slice header syntax with inherit flag slice_header( ) {Descriptor  . . . u(v)  if( !entropy_slice_flag ) {   slice_qp_deltase(v)   if (deblocking_filter_in_aps_enabled_flag &&  aps_deblocking_filter_flag) {   inherit_dbl_params_from_APS_flag u(1)/* Note that inherit_dbl_params_from_APS_flag = 0 is inferred ifdeblocking_filter_in_aps_enabled_flag = 0 oraps_deblocking_filter_flag=0. */   }   if(!inherit_dbl_params_from_APS_flag){    disable_deblocking_filter_flagu(1)    if (!disable_deblocking_filter_flag) {     beta_offset_div2se(v)     tc_offset_div2 se(v)    }   } . . .

As an alternative, Table 6 provides an exemplary portion of the sliceheader syntax including the inherit flag, i.e.,inherit_dbl_params_from_APS_flag, that is conditionally coded based onthe inherit enabled flag in the SPS syntax.

TABLE 6 Slice header syntax with inherit flag slice_header( ) {Descriptor  . . . u(v)  if( !entropy_slice_flag ) {   slice_qp_deltase(v)   if (deblocking_filter_in_aps_enabled_flag) {  inherit_dbl_params_from_APS_flag u(1) /* Note thatinherit_dbl_params_from_APS_flag = 0 is inferred ifdeblocking_filter_in_aps_enabled_flag = 0. */   }   if(!inherit_dbl_params_from_APS_flag){    disable_deblocking_filter_flagu(1)   if (!disable_deblocking_filter_flag) {    beta_offset_div2 se(v)   tc_offset_div2 se(v)    }  } . . .

Semantics for the slice header syntax of Tables 5 and 6 are defined asfollows. The disable_deblocking_filter_flag equal to 0 means that thedeblocking filter is enabled, and equal to 1 means that the deblockingfilter is disabled. The beta_offset_div2 and tc_offset_div2 syntaxelements indicate deblocking parameter offsets for t_(c) and β (dividedby 2). The inherit_dbl_params_from_APS_flag equal to 1 means thatdeblocking filter parameters present in the APS shall be used, and equalto 0 means that deblocking filter parameters that follow in the sliceheader shall be used.

A second issue with the signaling of deblocking filter parameters isthat no SPS level enable/disable flag is defined to indicate whether thedeblocking filter is enabled for pictures of the video sequence. Whenthe deblocking filter is disabled, no deblocking filter parameters areneeded to define the deblocking filter and coding the deblocking filterparameters is unnecessary. Table 7 provides an example of the SPS syntaxincluding the inherit enabled flag, i.e.,deblocking_in_aps_enabled_flag, conditionally coded based on adeblocking filter enabled flag, i.e., deblocking_filter_enabled_flag.

TABLE 7 SPS syntax with deblocking filter enabled flag and inheritenabled flag seq_parameter_set_rbsp( ) { Descriptor  profile_idc u(8) (omitted)  chroma_pred_from_luma_enabled_flag u(1) deblocking_filter_enabled_flag u(1)  if (deblocking_filter_enable_flag){   deblocking_filter_in_aps_enabled_flag u(1) /* Note that ifdeblocking_filter_enabled_flag=0, thendeblocking_filter_in_aps_enabled_flag=0 and aps_deblocking_filter_flag=0and disable_deblocking_filter_flag=1 are inferred */  } loop_filter_across_slice_flag u(1)  sample_adaptive_offset_enabled_flagu(1)  adaptive_loop_filter_enabled_flag u(1) pcm_loop_filter_disable_flag u(1)  cu_qp_delta_enabled_flag u(1) temporal_id_nesting_flag u(1)  inter_4x4_enabled_flag u(1) rbsp_trailing_bits( ) }

Semantics for the SPS syntax of Table 7 are defined as follows. Thedeblocking_filter_enabled_flag equal to 0 means that the deblockingfilter is disabled, and equal to 1 means that the deblocking filter isenabled.

In this way, when the deblocking filter is disabled at the SPS level, itmay be inferred that no deblocking parameters are signaled in the APS(i.e., the deblocking_filter_in_aps_enabled_flag in the SPS is equal to0 and the aps_deblocking_filter_flag in the APS is equal to 0). Inaddition, when the deblocking filter is disabled at the SPS level, itmay be inferred that the disable_deblocking_filter_flag in the sliceheader is equal to 1, indicating that the deblocking filter is disabledat the slice level.

Table 8 provides an example of the APS syntax in which the inheritenabled flag, i.e., aps_deblocking_filter_flag, is inferred to be equalto 0 when the deblocking filter is disabled at the SPS level.

TABLE 8 APS syntax with inherit enabled flag aps_rbsp( ) { Descriptor aps_id ue(v)  aps_deblocking_filter_flag u(1) aps_sample_adaptive_offset_flag u(1)  aps_adaptive_loop_filter_flagu(1)  if( aps_sample_adaptive_offset_flag || aps_adaptive_loop_filter_flag ) {   aps_cabac_use_flag u(1)   if(aps_cabac_use_flag ) {    aps_cabac_init_idc ue(v)   aps_cabac_init_qp_minus26 se(v)   }  }  if(aps_deblocking_filter_flag){   disable_deblocking_filter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_offset_div2 se(v)   tc_offset_div2 se(v)   }  } . . .

Table 9 provides an exemplary portion of the slice header syntaxincluding the deblocking filter parameters that are conditionally codedbased on the deblocking filter enabled flag, i.e.,deblocking_filter_enabled_flag, in the SPS syntax.

TABLE 9 Slice header syntax with inherit flag and conditionally codeddeblocking filter parameters slice_header( ) { Descriptor entropy_slice_flag u(1)  if( !entropy_slice_flag ) {   slice_type ue(v)  pic_parameter_set_id ue(v)   if( sample_adaptive_offset_enabled_flag|| adaptive_loop_filter_enabled_flag ||deblocking_filter_in_aps_enabled_flag )    aps_id ue(v)   frame_num u(v)  if( IdrPicFlag )    idr_pic_id ue(v)  .... u(v)  if(!entropy_slice_flag ) {   slice_qp_delta se(v)   if(deblocking_filter_in_aps_enabled_flag &&   aps_deblocking_filter_flag){   inherit_dbl_params_from_APS_flag u(1) /* Note thatinherit_dbl_params_from_APS_flag = 0 is inferred ifdeblocking_filter_in_aps_enabled_flag = 0 oraps_deblocking_filter_flag=0. */      }   if ((!inherit_dbl_params_from_APS_flag) &&  deblocking_filter_enabled_flag){   disable_deblocking_filter_flag u(1)     if(!disable_deblocking_filter_flag) {       beta_offset_div2 se(v)      tc_offset_div2 se(v)     }   } .....

As an alternative, instead of introducing a condition for coding thedeblocking filter parameters in the slice header based on the deblockingfilter enabled flag in the SPS, the techniques may infer that nodeblocking filter control syntax elements are signaled in the sliceheader when the deblocking filter is disabled at the SPS level. Acontrol present syntax element, i.e.,deblocking_filter_control_present_flag, included in the PPS syntax isdefined to indicate whether deblocking filter control syntax elements,including the deblocking filter parameters, are signaled in the sliceheader. In this case, the deblocking filter parameters are only coded inthe slice header when the deblocking filter control syntax elements aresignaled in the slice header, which only occurs when the deblockingfilter is enabled at the SPS level. The control present syntax elementin the PPS is proposed in Bross, W.-J. Han, J.-R. Ohm, G. J. Sullivan,T. Wiegand, “High efficiency video coding (HEVC) text specificationdraft 6,” 8^(th) JCT-VC Meeting, San Jose, Calif., USA, February 2012,which is also referred to as HEVC “Working Draft 6,” HEVC WD6, or simplyWD6.

Table 10 provides an example of the SPS syntax including the inheritenabled flag conditionally coded based on the deblocking filter enabledflag, and where a control present syntax element, i.e.,deblocking_filter_control_present_flag, in the PPS is inferred to beequal to 0 when the deblocking filter is disabled at the SPS level.

TABLE 10 SPS syntax with deblocking filter enabled flag and inheritenabled flag seq_parameter_set_rbsp( ) { Descriptor  profile_idc u(8) (omitted)  chroma_pred_from_luma_enabled_flag u(1) deblocking_filter_enabled_flag u(1)  if (deblocking_filter_enable_flag){  deblocking_filter_in_aps_enabled_flag u(1) Note that ifdeblocking_filter_enabled_flag=0, then it shall be inferred thatdeblocking_filter_in_aps_enabled_flag=0 and aps_deblocking_filter_flag=0and disable_deblocking_filter_flag=1 anddeblocking_filter_control_present_flag=0  } loop_filter_across_slice_flag u(1)  sample_adaptive_offset_enabled_flagu(1)  adaptive_loop_filter_enabled_flag u(1) pcm_loop_filter_disable_flag u(1)  cu_qp_delta_enabled_flag u(1) temporal_id_nesting_flag u(1)  inter_4x4_enabled_flag u(1) rbsp_trailing_bits( ) }

Table 11 provides an exemplary portion of the slice header syntaxincluding the deblocking filter parameters that are conditionally codedbased on the control present syntax element, i.e.,deblocking_filter_control_present_flag, in the PPS syntax.

TABLE 11 Slice header syntax with inherit flag and conditionally codeddeblocking filter parameters slice_header( ) { Descriptor  slice_typeue(v)  entropy_slice_flag u(1)  if( !entropy_slice_flag ) {  pic_parameter_set_id ue(v)   if(scaling_list_enable_flag ||  deblocking_filter_in_aps_enabled_flag ||  (sample_adaptive_offset_enabled_flag &&  !slice_sao_interleaving_flag) ||   adaptive_loop_filter_enabled_flag )    aps_id ue(v)  ....  if( !entropy_slice_flag ) {   slice_qp_deltase(v)  if( deblocking_filter_control_present_flag ) {   if(deblocking_filter_in_aps_enabled_flag) {  inherit_dbl_params_from_APS_flag u(1) /* Note thatinherit_dbl_params_from_APS_flag = 0 is inferred ifdeblocking_filter_in_aps_enabled_flag = 0. */   }    if ((!inherit_dbl_params_from_APS_flag) {    disable_deblocking_filter_flagu(1)       if (!disable_deblocking_filter_flag) {       beta_offset_div2 se(v)        tc_offset_div2 se(v)       }      } } .....

The difference between the example described with respect to Tables 10and 11 and the example described with respect to Tables 7-9 is that whenthe deblocking_filter_enable_flag in the SPS is equal to 0, thedeblocking_filter_control_present_flag in the PPS is also inferred to beequal to 0. In this way, the result of the deblocking filter beingdisabled at the SPS level is that no deblocking filter parameters willbe signaled in the APS or the slice header, and that the deblockingfilter is effectively disabled at the slice level. More specifically,when the deblocking filter is disabled at the SPS level, video decoder30 may infer that no deblocking filter parameters are present in the APS(i.e., the deblocking_filter_in_aps_enabled_flag in the SPS is equal to0 and the aps_deblocking_filter_flag in the APS is equal to 0) and thatno deblocking filter parameters are signaled in the slice header (i.e.,the deblocking_filter_control_present_flag in the PPS is equal to 0). Inaddition, video decoder 30 may infer that thedisable_deblocking_filter_flag in the slice header is equal to 1,indicating that the deblocking filter is disabled at the slice level. Inthis case, no additional conditions may need to be added in the sliceheader syntax because, when the deblocking_filter_control_present_flagin the PPS is equal to 0, none of the deblocking filter parameters aresignaled in the slice header.

A third issue with the signaling of deblocking filter parameters is thatno SPS level flag is defined to indicate when no deblocking filtercontrol syntax elements are signaled and default parameters, such aszero values, should be used to define the deblocking filter. When nodeblocking filter control syntax elements are signaled in either the APSor the slice header, no deblocking filter parameters are signaled todefine the deblocking filter. Table 12 provides an example of the SPSsyntax including the inherit enabled flag, i.e.,deblocking_in_aps_enabled_flag, conditionally coded based on a controlpresent syntax element, i.e., deblocking_filter_control_present_flag.

TABLE 12 SPS syntax with control present syntax element andconditionally coded inherit enabled flag seq_parameter_set_rbsp( ) {Descriptor  profile_idc u(8)  (omitted) chroma_pred_from_luma_enabled_flag u(1) deblocking_filter_control_present_flag u(1)  if(deblocking_filter_control_present_flag) {  deblocking_filter_in_aps_enabled_flag u(1) /* Note that ifdeblocking_filter_control_present_flag=0, thendeblocking_filter_in_aps_enabled_flag=0 and aps_deblocking_filter_flag=0and disable_deblocking_filter_flag=0 and beta_offset_div2=0 andtc_offset_div2=0 are inferred */  }  loop_filter_across_slice_flag u(1) sample_adaptive_offset_enabled_flag u(1) adaptive_loop_filter_enabled_flag u(1)  pcm_loop_filter_disable_flagu(1)  cu_qp_delta_enabled_flag u(1)  temporal_id_nesting_flag u(1) inter_4x4_enabled_flag u(1)  rbsp_trailing_bits( ) }

Table 13 provides an example of the APS syntax in which the inheritenabled flag, i.e., aps_deblocking_filter_flag, is inferred to be equalto 0 when no deblocking filter control syntax elements are present ineither the APS or the slice header, i.e., whendeblocking_filter_control_present_flag in the SPS syntax is equal to 0.

TABLE 13 APS syntax with inherit enabled flag aps_rbsp( ) { Descriptor aps_id ue(v)  aps_deblocking_fliter_flag u(1) aps_sample_adaptive_offset_flag u(1)  aps_adaptive_loop_filter_flagu(1)  if( aps_sample_adaptive_offset_flag || aps_adaptive_loop_filter_flag ) {   aps_cabac_use_flag u(1)   if(aps_cabac_use_flag ) {    aps_cabac_init_idc ue(v)   aps_cabac_init_qp_minus26 se(v)   }  }  if(aps_deblocking_filter_flag){   disable_deblocking_fllter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_(—) offset_div2 se(v)   tc_offset_div2 se(v)   }  } ....

Table 14 provides an example of the slice header syntax including thedeblocking filter parameters that are conditionally coded based on thecontrol present syntax element, i.e.,deblocking_filter_control_present_flag, in the SPS syntax.

TABLE 14 Slice header syntax with inherit flag and conditionally codeddeblocking filter parameters slice_header( ) { Descriptor entropy_slice_flag u(1)  if( !entropy_slice_flag ) {   slice_type ue(v)  pic_parameter_set_id ue(v)   if( sample_adaptive_offset_enabled_flag|| adaptive_loop_filter_enabled_flag ||deblocking_filter_in_aps_enabled_flag )    aps_id ue(v)   frame_num u(v)  if( IdrPicFlag )    idr_pic_id ue(v)  .... u(v)  if(!entropy_slice_flag ) {   slice_qp_delta se(v)   if(deblocking_filter_in_aps_enabled_flag &&   aps_deblocking_filter_flag){   inherit_dbl_params_from_APS_flag u(1) /* Note thatinherit_dbl_params_from_APS_flag = 0 is inferred ifdeblocking_filter_in_aps_enabled_flag = 0 oraps_deblocking_filter_flag=0. */   }   if ((!inherit_dbl_params_from_APS_flag) &&  deblocking_filter_control_present_flag){   disable_deblocking_filter_flag u(1)     if(!disable_deblocking_filter_flag) {       beta_offset_div2 se(v)      tc_offset_div2 se(v)     }    } .....

FIG. 4 is a block diagram illustrating components of an exemplarydeblocking filter 100 defined based on deblocking filter parameterssignaled according to the techniques described in this disclosure. Ingeneral, either or both of deblocking filter 63 from FIG. 2 anddeblocking filter 91 from FIG. 3 may include components substantiallysimilar to those of deblocking filter 100. Other video coding devices,such as video encoders, video decoders, video encoder/decoders (CODECs),and the like may also include components substantially similar todeblocking filter 100. Deblocking filter 100 may be implemented inhardware, software, or firmware, or any combination thereof. Whenimplemented in software or firmware, corresponding hardware (such as oneor more processors or processing units and memory for storinginstructions for the software or firmware) may also be provided.

In the example of FIG. 4, deblocking filter 100 includes deblockingdetermination unit 104, support definitions 102 stored in memory,deblocking filtering unit 106, deblocking filter definitions 108 storedin memory, edge locating unit 103, and edge locations data structure105. Any or all of the components of deblocking filter 100 may befunctionally integrated. The components of deblocking filter 100 areillustrated separately only for purposes of illustration. In general,deblocking filter 100 receives data for decoded blocks, e.g., from asummation component that combines prediction data with residual data forthe blocks. The data may further include an indication of how the blockswere predicted. In the example described below, deblocking filter 100 isconfigured to receive data including a decoded vide block associatedwith a LCU and a CU quadtree for the LCU, where the CU quadtreedescribes how the LCU is partitioned into CUs and prediction modes forPUs and TUs of leaf-node CUs.

Deblocking filter 100 may maintain edge locations data structure 105 ina memory of deblocking filter 100, or in an external memory provided bya corresponding video coding device. In some examples, edge locatingunit 103 may receive a CU quadtree corresponding to an LCU thatindicates how the LCU is partitioned into CUs. Edge locating unit 103may then analyze the CU quadtree to determine edges between decodedvideo blocks associated with TUs and PUs of CUs in the LCU that arecandidates for deblocking.

Edge locations data structure 105 may comprise an array having ahorizontal dimension, a vertical dimension, and a dimensionrepresentative of horizontal edges and vertical edges. In general, edgesbetween video blocks may occur between two video blocks associated withsmallest-sized CUs of the LCU, or TUs and PUs of the CUs. Assuming thatthe LCU has a size of N×N, and assuming that the smallest-sized CU ofthe LCU is of size M×M, the array may comprise a size of [N/M]×[N/M]×2,where “2” represents the two possible directions of edges between CUs(horizontal and vertical). For example, assuming that an LCU has 64×64pixels and a 8×8 smallest-sized CU, the array may comprise [8]×[8]×[2]entries.

Each entry may generally correspond to a possible edge between two videoblocks. Edges might not in fact exist at each of the positions withinthe LCU corresponding to each of the entries of edge locations datastructure 105. Accordingly, values of the data structure may beinitialized to false. In general, edge locating unit 103 may analyze theCU quadtree to determine locations of edges between two video blocksassociated with TUs and PUs of CUs of the LCU and set correspondingvalues in edge locations data structure 105 to true.

In general, the entries of the array may describe whether acorresponding edge exists in the LCU as a candidate for deblocking. Thatis, when edge locating unit 103 determines that an edge between twoneighboring video blocks associated with TUs and PUs of CUs of the LCUexists, edge locating unit 103 may set a value of the correspondingentry in edge locations data structure 105 to indicate that the edgeexists (e.g., to a value of “true”).

Deblocking determination unit 104 generally determines whether, for twoneighboring blocks, an edge between the two blocks should be deblocked.Deblocking determination unit 104 may determine locations of edges usingedge locations data structure 105. When a value of edge locations datastructure 105 has a Boolean value, deblocking determination unit 104 maydetermine that a “true” value indicates the presence of an edge, and a“false” value indicates that no edge is present, in some examples.

In general, deblocking determination unit 104 is configured with one ormore deblocking determination functions. The functions may include aplurality of coefficients applied to lines of pixels that cross the edgebetween the blocks. For example, the functions may be applied to a lineof eight pixels that is perpendicular to the edge, where four of thepixels are in one of the two blocks and the other four pixels are in theother of the two blocks. Support definitions 102 define support for thefunctions. In general, the “support” corresponds to the pixels to whichthe functions are applied. Various examples of sets of support aredescribed in greater detail below with respect to FIG. 5.

Deblocking determination unit 104 may be configured to apply one or moredeblocking determination functions to one or more sets of support, asdefined by support definitions 102, to determine whether a particularedge between two blocks of video data should be deblocked. The dashedline originating from deblocking determination unit 104 represents datafor blocks being output without being filtered. In cases wheredeblocking determination unit 104 determines that an edge between twoblocks should not be filtered, deblocking filter 100 may output the datafor the blocks without altering the data. That is, the data may bypassdeblocking filtering unit 106. On the other hand, when deblockingdetermination unit 104 determines that an edge should be deblocked,deblocking determination unit 104 may cause deblocking filtering unit106 to filter values for pixels near the edge in order to deblock theedge.

Deblocking filtering unit 106 retrieves definitions of deblockingfilters from deblocking filter parameters 108 for edges to be deblocked,as indicated by deblocking determination unit 104. In general, filteringof an edge uses values of pixels from the neighborhood of a current edgeto be deblocked. Therefore, both deblocking decision functions anddeblocking filters may have a certain support region on both sides of anedge. By applying a deblocking filter to pixels in the neighborhood ofan edge, deblocking filtering unit 106 may smooth the values of thepixels such that high frequency transitions near the edge are dampened.In this manner, application of deblocking filters to pixels near an edgemay reduce blockiness artifacts near the edge.

FIG. 5 is a conceptual diagram illustrating pixel positions near an edge134 of a video block between sub-blocks 130 and 132. As one example,edge 134 may comprise an inner CU edge such as a TU edge between two TUsdefined in the CU, or a PU edge between two PUs defined in the CU. Eachof the pixel positions is designated using the format [p|q]I_(J), wherep corresponds to sub-block 130 and q corresponds to sub-block 132, Icorresponds to a distance from edge 134, and J corresponds to a rowindicator from top to bottom of sub-blocks 130 and 132. In someexamples, support used for deblocking decision functions and deblockingfilters has a line of eight pixels. In such examples, for a given line Xwhere 0≦X≦7, each of pixels p3_(X) to q3_(X) may be used as support.

FIG. 6 is a flowchart illustrating an example operation of encodingdeblocking filter parameters for a current video slice with reducedbitstream overhead in accordance with the techniques described in thisdisclosure. The operation illustrated in FIG. 6 is described withrespect to video encoder 20 from FIG. 2.

Entropy encoding unit 56 of video encoder 20 encodes a first syntaxelement defined to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header forpictures referring to the picture layer parameter set (140). Ifdeblocking filter parameters are not present in both the picture layerparameter set and the slice header (NO branch of 141), entropy encodingunit 56 eliminates encoding of a second syntax element in the sliceheader (142). The second syntax element is defined to indicate which setof deblocking filter parameters to use to define a deblocking filter fora current video slice. In the case where deblocking filter parametersare only present in one of the picture layer parameter set or the sliceheader, the second syntax element is unnecessary because no decisionneeds to made regarding which deblocking filter parameters to use todefine the deblocking filter. Instead, deblocking filter 63 is definedfor the current video slice based on the single set of deblocking filterparameters that are present in either the picture layer parameter set orthe slice header (144).

If deblocking filter parameters are present in both the picture layerparameter set and the slice header (YES branch of 141), entropy encodingunit 56 encodes the second syntax element in the slice header, which isdefined to indicate whether to use a first set of deblocking parametersincluded in the picture layer parameter set or a second set ofdeblocking parameters included in the slice header (146). In this case,deblocking filter 63 is defined for the current video slice based on theindicated set of deblocking parameters (148). According to thetechniques described in this disclosure, therefore, deblocking filterparameters are encoded for a current video slice with reduced bitstreamoverhead by only encoding the second syntax element in the slice headerwhen deblocking filter parameters are present in both the picture layerparameter set and the slice header.

FIG. 7 is a flowchart illustrating an example operation of decodingdeblocking filter parameters for a current video slice with reducedbitstream overhead in accordance with the techniques described in thisdisclosure. The operation illustrated in FIG. 7 is described withrespect to video decoder 30 from FIG. 3.

Entropy decoding unit 80 of video decoder 30 decodes a first syntaxelement configured to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header forpictures referring to the picture layer parameter set (150). Ifdeblocking filter parameters are not present in both the picture layerparameter set and the slice header (NO branch of 151), entropy decodingunit 80 determines that a second syntax element is not present in theslice header to be decoded (152). The second syntax element is definedto indicate which set of deblocking filter parameters to use to define adeblocking filter for a current video slice. In the case wheredeblocking filter parameters are only present in one of the picturelayer parameter set or the slice header, the second syntax element isunnecessary because no decision needs to made regarding which deblockingfilter parameters to use to define the deblocking filter. Instead,deblocking filter 91 is defined for the current video slice based on thesingle set of deblocking filter parameters that are present in eitherthe picture layer parameter set or the slice header (154).

If deblocking filter parameters are present in both the picture layerparameter set and the slice header (YES branch of 151), entropy decodingunit 80 decodes the second syntax element in the slice header, which isdefined to indicate whether to use a first set of deblocking parametersincluded in the picture layer parameter set or a second set ofdeblocking parameters included in the slice header (156). In this case,deblocking filter 91 is defined for the current video slice based on theindicated set of deblocking parameters (158). According to thetechniques described in this disclosure, therefore, deblocking filterparameters are decoded for a current video slice with reduced bitstreamoverhead by only decoding the second syntax element in the slice headerwhen deblocking filter parameters are present in both the picture layerparameter set and the slice header.

FIG. 8 is a flowchart illustrating an example operation of encodingdeblocking filter parameters for a current video slice in a pictureparameter set (PPS) that may be overridden by deblocking filterparameters in a slice header. The operation illustrated in FIG. 8 isdescribed with respect to video encoder 20 from FIG. 2.

Entropy encoding unit 56 encodes a control present syntax element in thePPS defined to indicate whether any deblocking filter control syntaxelements are present in the PPS and the slice header (160). Thedeblocking filter control syntax elements include an override enabledflag signaled in the PPS, an override flag signaled in the slice header,and deblocking filter parameters signaled in the PPS and/or the sliceheader. When deblocking filter control syntax elements are not presentin either the PPS or the slice header (NO branch of 162), entropyencoding unit 56 eliminates encoding any of the deblocking filtercontrol syntax elements (164). In this case, video encoder 20 signals tovideo decoder 30 that deblocking filter 63 is not defined based on codeddeblocking filter parameters. Instead, deblocking filter 63 is definedbased on default deblocking filter parameters (166).

When deblocking filter control syntax elements are present in the PPS orthe slice header (YES branch of 162), entropy encoding unit 56 encodesan override enabled flag in the PPS that indicates whether an overrideof a first set of deblocking filter parameters included in the PPS by asecond set of deblocking filter parameters included in the slice headeris enabled (168).

If the override of the deblocking filter parameters in the PPS is notenabled (NO branch of 170), entropy encoding unit 56 eliminates encodingof an override flag in the slice header (172). The override flagindicates which set of deblocking filter parameters to use to define adeblocking filter for a current video slice. In the case wheredeblocking filter parameters are only present in the PPS, the overrideflag in the slice header is unnecessary because no decision needs to bemade regarding which deblocking filter parameters to use to define thedeblocking filter. Instead, deblocking filter 63 is defined for thecurrent video slice based on the deblocking filter parameters present inthe PPS (174).

If the override of the deblocking filter parameters in the PPS by thedeblocking parameters in the slice header is enabled (YES branch of170), entropy encoding unit 56 encodes the override flag in the sliceheader that indicates whether to use the first set of deblocking filterparameters from the PPS or to override the first set of deblockingfilter parameters with the second set of deblocking filter parametersincluded in the slice header (176). In this case, deblocking filter 63is defined for the current video slice based on the indicated set ofdeblocking parameters (178).

FIG. 9 is a flowchart illustrating an example operation of decodingdeblocking filter parameters for a current video slice in a pictureparameter set (PPS) that may be overridden by deblocking filterparameters in a slice header. The operation illustrated in FIG. 9 isdescribed with respect to video decoder 30 from FIG. 3.

Entropy decoding unit 80 decodes a control present syntax element in thePPS defined to indicate whether any deblocking filter control syntaxelements are present in the PPS and the slice header (180). Thedeblocking filter control syntax elements include an override enabledflag signaled in the PPS, an override flag signaled in the slice header,and deblocking filter parameters signaled in the PPS and/or the sliceheader. When deblocking filter control syntax elements are not presentin either the PPS or the slice header (NO branch of 182), entropydecoding unit 80 determines that no deblocking filter control syntaxelements are present in the bitstream to be decoded (184). In this case,video decoder 30 knows that deblocking filter 91 is not defined based oncoded deblocking filter parameters. Instead, deblocking filter 91 isdefined based on default deblocking filter parameters (186).

When deblocking filter control syntax elements are present in the PPS orthe slice header (YES branch of 182), entropy decoding unit 80 decodesan override enabled flag in the PPS that indicates whether an overrideof a first set of deblocking filter parameters included in the PPS by asecond set of deblocking filter parameters included in the slice headeris enabled (188).

If the override of the deblocking filter parameters in the PPS is notenabled (NO branch of 190), entropy decoding unit 80 determines that anoverride flag is not present in the slice header to be decoded (192).The override flag indicates which set of deblocking filter parameters touse to define a deblocking filter for a current video slice. In the casewhere deblocking filter parameters are only present in the PPS, theoverride flag in the slice header is unnecessary because no decisionneeds to be made regarding which deblocking filter parameters to use todefine the deblocking filter. Instead, deblocking filter 91 is definedfor the current video slice based on the deblocking filter parameterspresent in the PPS (194).

If the override of the deblocking filter parameters in the PPS by thedeblocking parameters in the slice header is enabled (YES branch of190), entropy decoding unit 80 decodes the override flag in the sliceheader that indicates whether to use the first set of deblocking filterparameters from the PPS or to override the first set of deblockingfilter parameters with the second set of deblocking filter parametersincluded in the slice header (196). In this case, deblocking filter 91is defined for the current video slice based on the indicated set ofdeblocking parameters (198).

In the examples described above in which a set of deblocking filterparameters are included in an APS, the APS may be signaled to videodecoder 30 anytime parameters change for ALF, SAO or deblocking ALF andSAO parameters likely change more frequently than deblocking filterparameters. In this case, bits may be wasted when the same deblockingfilter parameters are repeated in the APS whenever the SAO or ALFparameters change. As one solution to reduce APS bitstream overhead, insome examples, the techniques introduce multiple APSs to update thedeblocking filter parameters separately from the ALF and SAO parameters.To avoid signaling copies of constant deblocking parameters insubsequent APSs, the slice header may refer to multiple APSs to decodevideo data of the slices. Several options for using multiple APSs tosignal deblocking filter parameters as described below. Syntax of APSsand slice headers are presented in tables below in which strikethroughsrepresent syntax elements and conditions that may be removed from theAPS and slice header syntax.

As a first example, the slice header may reference multiple differentAPSs using unique APS identifiers, e.g., aps_id[i], for each valid APS.In this case, the techniques include deblocking filter parameters in amultiple APS approach, e.g., where the multiple APS approach may besimilar to that proposed in M. Li, P. Wu, “Multiple Adaptation ParameterSets Referring,” 7^(th) JCT-VC Meeting, Geneva, Switzerland, November2011, Doc. JCTVC-G332.

TABLE 15 Slice header syntax with APS identifiers slice_header( ) {Descriptor  ...... ...  lightweight_slice_flag u(1)  if(!lightweight_slice_flag ) {   slice_type ue(v)   pic_parameter_set_idue(v)  if( sample_adaptive_offset_enabled_flag ||adaptive_loop_filter_enabled_flag ||deblocking_filter_in_aps_enabled_flag) {   number_of_valid_aps u(v)   if(number_of_valid_aps != 0 ) {    for (i = 0; i < number_of_valid_aps;i++) {     aps_id[i] ue(v)    }   }  }   ......  }  ...... }

Semantics for the slice header syntax of Table 15 are defined asfollows. The deblocking_filter_enabled_flag equal to 0 means that thedeblocking filter is disabled, and equal to 1 means that the deblockingfilter is enabled. The number_of_valid_aps syntax element specifies thenumber of valid APSs for decoding the slice. The value of thenumber_of_valid_aps shall be in the range of [0, MaxNumberValidAps],inclusively. The value of the MaxNumberValidAps is specified inProfile/Level. If the number_of_valid_aps does not exist, its value isinferred to be 0. If the number_of_valid_aps is equal to 0, it isinferred as no active APSs. The aps_id[i] specifies the valid APS IDsfor decoding the slice, where i shall be in the range of [0,number_of_valid_aps−1], inclusive.

According to the above slice header syntax, the decoding rules for aslice according to potentially multiple APSs are as follows. When thenumber_of_valid_aps value equals 0 or is not presented, i.e., no APS isreferred to in slice header, the flags ofaps_sample_adaptive_offset_flag and aps_adaptive_loop_filter_flag andaps_deblocking_filter_flag in decoding this slice shall be set to 0, andneither SAO nor ALF shall be applied in decoding the slice. If the valueof inherit_dbl_params_from_APS_flag equals 0, then the deblocking filtershall be applied in decoding this slice and the deblocking parametersincluded in this slice header shall be used.

When the number_of_valid_aps value equals to 1, i.e., only one APS isreferred to in the slice header, the flags ofaps_sample_adaptive_offset_flag and aps_adaptive_loop_filter_flag andaps_deblocking_filter_flag and the tool parameters of SAO and ALF indecoding this slice shall be set equal to the values of thecorresponding syntax elements presented in this referred APS. If thevalue of inherit_dbl_params_from_APS_flag equals 1, then the deblockingparameters shall be set equal to the values of corresponding parametersin the referred APS.

When number_of_valid_aps is larger than 1, i.e., when the multiple APSsapproach is applied, for the deblocking filter, if all theaps_deblocking_filter_flag elements in the referred APSs are equal to 0,the aps_deblocking_filter_flag in decoding this slice shall be set to 0and, if inherit_dbl_params_from_APS_flag equals 0, then the deblockingfilter shall be applied to this slice using the deblocking parameterspresent in this slice header. Otherwise, if one and only one APScontains the aps_deblocking_filter_flag equal to 1, theaps_deblocking_filter_flag in decoding this slice shall be set to 1 andif inherit_dbl_params_from_APS_flag equals 1, then the deblocking filterwith the deblocking parameters parsed from this APS shall be applied indecoding this slice. Otherwise, if there are more than one APScontaining aps_deblocking_filter_flag equal to 1, theaps_deblocking_filter_flag in decoding this slice shall be set to 0 andif inherit_dbl_params_from_APS_flag equals 0 then the deblocking filtershall be applied to this slice using the deblocking parameters presentin this slice header.

According to the techniques of this disclosure, theaps_deblocking_filter_flag can indicate that deblocking parameters arepresent in the APS, as provided in Table 16 below.

TABLE 16 APS syntax with inherit enabled flag aps_rbsp( ) { Descriptor aps_id ue(v)  aps_deblocking_filter_flag u(1) aps_sample_adaptive_offset_data_present_flag u(1) aps_adaptive_loop_filter_data_present_flag u(1)  if(aps_sample_adaptive_offset_data_present_flag ||  aps_adaptive_loop_filter_data_present_flag ) {   aps_cabac_use_flagu(1)   if( aps_cabac_use_flag ) {    aps_cabac_init_idc ue(v)   aps_cabac_init_qp_minus26 se(v)   }  }  if(aps_deblocking_filter_flag){   disable_deblocking_filter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_(—) offset_div2 se(v)   tc_offset_div2 se(v)   }  }  if(aps_adaptive_loop_filter_data_present_flag ) {  aps_adaptive_loop_filter_flag u(1)   if(aps_adaptive_loop_filter_flag) {    alf_data_byte_count u(8)   alf_param( )    byte_align( )   }  }  if(aps_sample_adaptive_offset_data_present_flag ) {  aps_sample_adaptive_offset_flag u(1)   if (aps_sample_adaptive_offset_(—) flag ) {    sao_data_byte_count u(8)   byte_align ( )    sao_param( )   }  }  rbsp_trailing_bits( ) }

Semantics for the APS syntax of Table 16 are defined as follows. Theaps_sample_adaptive_offset_data_present_flag equal to 1 specifies thatthe SAO parameters exist in this APS, and equal to 0 specifies that theSAO parameters do not exist in this APS, where the SAO parameters referto the SAO enable flag and SAO parameters when SAO enable flag is 1.

The aps_sample_adaptive_offset_flag equal to 1 specifies that the SAO ison for slices referred to the current APS, and equal to 0 specifies thatthe SAO is off for slices referred to the current APS. If there is noactive APS or the aps_sample_adaptive_offset_flag value equals to 0, theaps_sample_adaptive_offset_flag value is inferred to be 0.

The aps_adaptive_loop_filter_data_present_flag equal to 1 specifies thatthe ALF parameters exist in this APS, and equal to 0 specifies that theALF parameters does not exist in this APS, where the ALF parametersrefer to the ALF enable flag and ALF parameters when ALF enable flagis 1. The aps_adaptive_loop_filter_flag equal to 1 specifies that theALF is on for slices referred to the current APS, and equal to 0specifies that the ALF is off for slices referred to the current APS. Ifthere is no active APS or the aps_adaptive_loop_filter_data_present_flagvalue equals to 0, the aps_adaptive_loop_filter_flag value is inferredto be 0.

According to the above APS syntax, the decoding rules for a sliceaccording to potentially multiple APSs are as follows. Whennumber_of_valid_aps is larger than 1 (other cases as before), the APSwith its ID equal to aps_id[0] can be hypothetically taken as the basicAPS in decoding the current slice, while the other APSs with their IDsequal to aps_id[1], aps_id[2], . . . aps_id[number_valid_aps−1] can betaken as the amended APSs. The presented information in the amended APSswith its APS ID of aps_id[i] (i>0), which refers to the tool parameters(i.e. aps_deblocking_filter_flag and deblocking parameters fordeblocking filter and/or aps_sample_adaptive_offset_flag and sao_param() for SAO and/or aps_adaptive_loop_filter_flag and alf_param( ) for ALF)presented in an APS when aps_deblocking_filter_flag equals 1 and/oraps_sample_adaptive_offset_data_present_flag is 1 and/oraps_adaptive_loop_filter_data_present_flag is 1, overwrites theinformation of the corresponding tools formerly and temporallydetermined by the APSs with their APS ID of aps_id[i−1], . . . ,aps_id[0]. Thereby, the finally obtained values ofaps_deblocking_filter_flag and of deblocking parameters are used fordeblocking the current slice (additionally dependent on value ofinherit_dbl_params_from_APS_flag). The finally obtainedaps_sample_adaptive_offset_flag and the parameters in sao_param( ) areused for implementing SAO in decoding the current slice, and the finallyobtained aps_adaptive_loop_filter_flag and the parameters in alf_param() are used for implementing ALF in decoding the current slice.

In other words, when multiple APSs are referred to by a slice, for eachtool, according to the presentation order of the APS IDs, the last APSthat contains the data_present_flag (i.e. aps_deblocking_filter_flag oraps_sample_adaptive_offset_data_present_flag oraps_adaptive_loop_filter_data_present_flag) of this tool equal to 1 isactivated to initialize this tool before decoding this slice.

As a second example for using multiple APSs to signal deblocking filterparameters, the slice header may reference multiple different sub-APSsusing unique sub-APS identifiers for each type of APS. In this case, thetechniques include deblocking filter parameters in a sub-APS approachsuch as that proposed in J. Tanaka, Y. Morigami, T. Suzuki, “Non-CE4Subtest3: Extension of Adaptation Parameter Sets syntax for Quantizationmatrix,” 7^(th) JCT-VC Meeting, Geneva, Switzerland, November 2011, Doc.JCTVC-G295.

According to the techniques of this disclosure, it is proposed toinclude the aps_dbl_id in the APS, as follows in Tables 17 and 18. Ifthe inherit_dbl_params_from_APS_flag=1 then the deblocking parametersare copied from the APS with aps_dbl_id.

TABLE 17 APS syntax with inherit enabled flag and conditionally codeddeblocking APS ID aps_rbsp( ) { Descriptor  aps_id ue(v) aps_deblocking_filter_flag u(1)  aps_sample_adaptive_offset_flag u(1) aps_adaptive_loop_filter_flag u(1) ....  if(aps_deblocking_filter_flag){   aps_dbl_id ue(v)  disable_deblocking_filter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_(—) offset_div2 se(v)   tc_offset_div2 se(v)   }  }   if( aps_sample_adaptive_offset_flag ) {   aps_sao_id ue(v)    sao_data_byte_count u(8)    byte_align ( )   sao_param( )    byte_align ( )  }   if( aps_adaptive_loop_filter_flag) {    aps_alf_id ue(v)    alf_data_byte_count u(8)    byte_align ( )   alf_param( )    byte_align( )  }   rbsp_trailing_bits( ) }

TABLE 18 Slice header syntax with sub-APS identifiers slice_header( ) {Descriptor  entropy_slice_flag u(1)  if( !entropy_slice_flag ) {  slice_type ue(v)   pic_parameter_set_id ue(v)   

 

   

  if (deblocking_filter_in_aps_enabled_flag)    aps_dbl_id ue(v)   if(sample_adaptive_offset_enabled_flag)    aps_sao_id ue(v)  if(adaptive_loop_filter_enabled_flag)    aps_alf_id ue(v)   if(quantization_matrix_enabled_flag)    aps_qmatrix_id ue(v)    frame_numu(v) .......  if( !entropy_slice_flag ) {   slice_qp_delta se(v)  inherit_dbl_params_from_APS_flag u(1)   if(!inherit_dbl_params_from_APS_flag){    disable_deblocking_filter_flagu(1)      if (!disable_deblocking_filter_flag) {       beta_offset_div2se(v)       tc_offset_div2 se(v)     }    }   if( slice_type = = B )   collocated_from_l0_flag u(1)   if( adaptive_loop_filter_enabled_flag&&   aps_adaptive_loop_filter_flag ) {    byte_align( )   alf_cu_control_param( )    byte_align( )   }   if( (weighted_pred_flag && slice_type = = P) ||    ( weighted_bipred_idc = =1 && slice_type = =    B ) ) pred_weight_table( )  }  if( slice_type = =P || slice_type = = B )   5_minus_max_num_merge_cand ue(v)  for( i = 0;i < num_substreams_minus1 + 1; i++ ){   substream_length_mode u(2)  substream_length[i] u(v)  } }

The problem with the slice header syntax above is that the aps_dbl_id issignaled even when the inherit_dbl_params_from_APS_flag=0. As analternative, the aps_dbl_id may be signaled in the slice header asprovided in Table 19 below.

TABLE 19 Slice header syntax with conditionally coded sub-APSidentifiers slice_header( ) { Descriptor  entropy_slice_flag u(1)  if(!entropy_slice_flag ) {   slice_type ue(v)   pic_parameter_set_id ue(v)  

 

   

  if( sample_adaptive_offset_enabled_flag)    aps_sao_id ue(v)  if(adaptive_loop_filter_enabled_flag)    aps_alf_id ue(v)   if(quantization_matrix_enabled_flag)    aps_qmatrix_id ue(v)    frame_numu(v)   .....  if( !entropy_slice_flag ) {   slice_qp_delta se(v)  inherit_dbl_params_from_APS_flag u(1)   if(inherit_dbl_params_from_APS_flag) {    aps_dbl_id ue(v)    }   if(!inherit_dbl_params_from_APS_flag){    disable_deblocking_filter_flagu(1)     if (!disable_deblocking_filter_flag) {      beta_offset_div2se(v)      tc_offset_div2 se(v)     }   } .....

As a third example for using multiple APSs to signal deblocking filterparameters, the slice header may reference multiple different APSs usinglinked-list APSs. In this case, the techniques include deblocking filterparameters in the APS referencing method based on linked-list APSs,e.g., as described in M. Li, P. Wu, S. Wenger, J. Boyce, “APSReferencing,” 8^(th) JCT-VC Meeting, San Jose, February 2011.

The APS Referencing document builds upon the partial APS update methodproposed in JCTVC-G332 in the sense that it also introduces flags in theAPS to signal the presence of loop filter and scaling list parameters.In addition, the ref_aps_flag and ref_aps_id syntax elements areintroduced in the APS to enable the partial update of parameters througha linked list mechanism. According to the techniques of this disclosure,the aps_deblocking_filter_flag can indicate that deblocking parametersare present in the APS, as provided in Table 20 below. Associatedchanges to the syntax of the slice header are provided in Table 21below.

TABLE 20 APS syntax with inherit enabled flag and linked-list APSsaps_rbsp( ) { Descriptor  aps_id ue(v)  ref_aps_flag u(1) if(ref_aps_flag) {   ref_aps_id ue(v)  }  aps_deblocking_filter_flagu(1)  aps_scaling_list_data_present_flag u(1) aps_sample_adaptive_offset_data_present_flag u(1) aps_adaptive_loop_filter_data_present_flag u(1) ........  if(aps_deblocking_filter_flag){   disable_deblocking_filter_flag u(1)   if(!disable_deblocking_filter_flag) {    beta_(—) offset_div2 se(v)   tc_offset_div2 se(v)   }  }  if(aps_scaling_list_data_present_flag) {  

  

  scaling_list_param( )   

 }  if( aps_sample_adaptive_offset_data_present_flag ) {    

   

   sao_param( )    

 }  if( aps_adaptive_loop_filter_data_present_flag ) {   

  

  alf_param( )  }  rbsp_trailing_bits( ) }

TABLE 21 Slice header syntax with linked-list APS identifiersslice_header( ) { Descriptor  lightweight_slice_flag u(1)  if(!lightweight_slice_flag ) {   slice_type ue(v)   pic_parameter_set_idue(v)  if( scaling_list_enabled_flag ||   sample_adaptive_offset_enabled_flag ||   adaptive_loop_filter_enabled_flag ||  deblocking_filter_in_aps_enabled_flag) aps_id ue(v)   ......   if(deblocking_filter_in_aps_enabled_flag &&   aps_deblocking_filter_flag){   inherit_dbl_params_from_APS_flag u(1)  /* Note thatinherit_dbl_params_from_APS_flag = 0 is  inferred ifdeblocking_filter_in_aps_enabled_flag = 0 or aps_deblocking_filter_flag=0. */    }    if(!inherit_dbl_params_from_APS_flag){     disable_deblocking_filter_flagu(1)      if (!disable_deblocking_filter_flag) {       beta_offset_div2se(v)       tc_offset_div2 se(v)      }      }  if(scaling_list_enabled_flag)   scaling_list_flag u(1)  if(sample_adaptive_offset_enabled_flag)   sample_adaptive_offset_flag u(1) if (adaptive_loop_filter_enabled_flag)   adaptive_loop_filter_flag u(1) }  ...... }

Semantics for the APS and slice header syntax of Tables 20 and 21 aredefined as follows. The aps_id identifies the adaptation parameter setthat is referred to by the slice header or by the ref_aps_id in anotheradaptation parameter set. The value of aps_id shall be in the range of 0to 7, inclusive. The ref_aps_flag equal to 1 specifies that thisadaptation parameter set references another adaptation parameter set.The ref_aps_flag equal to 0 specifies that this adaptation parameter setdoes not reference any other adaptation parameter set. The ref_aps_idspecifies that the previous adaptation parameter set with aps_id equalto ref_aps_id is referenced by this adaptation parameter set.

The aps_deblocking_filter_flag indicates that deblocking parameters arepresent in the APS (equal to 1) or not present (equal to 0). Theaps_scaling_list_data_present_flag equal to 1 specifies that scalinglist parameters are present in this adaptation parameter set, and equalto 0 specifies that scaling list parameters are not present in thisadaptation parameter set. Theaps_sample_adaptive_offset_data_present_flag equal to 1 specifies thatSAO parameters are present in this adaptation parameter set, and equalto 0 specifies that SAO parameters are not present in this adaptationparameter set. The aps_adaptive_loop_filter_data_present_flag equal to 1specifies that the ALF parameters are present in this adaptationparameter set, and equal to 0 specifies that the ALF parameters are notpresent in this adaptation parameter set.

The scaling_list_flag equal to 1 specifies that the scaling matrix isapplied for the current slice, and equal to 0 specifies that the scalingmatrix is not applied for the current slice. The value ofscaling_list_flag_flag shall be the same for all slices in the currentframe. The adaptive_loop_filter_flag equal to 1 specifies that theadaptive loop filter is applied for the current slice, and equal to 0specifies that the adaptive loop filter is not applied for the currentslice. The value of adaptive_loop_filter_flag shall be the same for allslices in the current frame. The sample_adaptive_offset_flag equal to 1specifies that sample adaptive offset is applied for the current slice,and equal to 0 specifies that sample adaptive offset is not applied forthe current slice. The value of sample_adaptive_offset_flag shall be thesame for all slices in the current frame.

As a fourth option for using multiple APSs to signal deblocking filterparameters, the slice header may include partial updates of deblockingfilter parameters specified in the APS. In this case, the techniquesinclude partial updates of deblocking filter parameters. Thesetechniques may be applied, for example, in the method of updating APSparameters using slice header signaling described in A. Minezawa, K.Sugimoto, S.-I. Sekiguchi, “On partial updating of APS parameters,”8^(th) JCT-VC Meeting, San Jose, Calif., USA, February 2012, Doc.JCTVC-H0255.

The techniques of this disclosure may update the deblocking filteradjustment parameters in the APS identified by the aps_id in the sliceheader based on deblocking filter adjustment parameters included in theslice header. The techniques may introduce anupdate_dbl_params_in_APS_flag in the slice header to indicate whendeblocking filter adjustment parameters in the APS are to be updated bythe deblocking filter adjustment parameters in the slice header, aspresented in Table 22 below.

TABLE 22 Slice header syntax with update deblocking parameters in APSflag slice_header( ) { Descriptor  entropy_slice_flag u(1)  if(!entropy_slice_flag ) {   slice_type ue(v)   pic_parameter_set_id ue(v)  if( sample_adaptive_offset_enabled_flag ||  adaptive_loop_filter_enabled_flag )    aps_id ue(v)  ....  if(!entropy_slice_flag ) {   slice_qp_delta se(v)  inherit_dbl_params_from_APS_flag u(1)   update_dbl_params_in_APS_flagu(1)  if ( (!inherit_dbl_params_from_APS_flag) || update_dbl_params_in_APS_flag ) {    disable_deblocking_filter_flagu(1)    if ( !disable_deblocking_filter_flag ) {     beta_offset_div2se(v)     tc_offset_div2 se(v)    }   }  ..... }

Semantics for the slice header syntax of Table 22 are defined asfollows. The update_dbl_params_in_APS_flag equal to 1 means that thedeblocking filter adjustment parameters in the APS with ID equal toaps_id shall be updated with the deblocking filter adjustment parametersin the slice header, and equal to 0 means no update.

In addition, techniques of this disclosure may include updating thedeblocking filter adjustment parameters in the APS identified by theaps_dbl_id in the slice header based on deblocking filter adjustmentparameters included in the slice header. The aps_dbl_id of the APS to beupdated with the slice header deblocking filter adjustment parametersmay be signaled separately in the slice header, as presented in Table 23below.

TABLE 23 Slice header syntax with update deblocking parameters in APSflag and sub-APS identifiers slice_header( ) { Descriptor entropy_slice_flag u(1)  if( !entropy_slice_flag ) {   slice_type ue(v)  pic_parameter_set_id ue(v)   if( sample_adaptive_offset_enabled_flag||   adaptive_loop_filter_enabled_flag )    aps_id ue(v)  ....  if(!entropy_slice_flag ) {   slice_qp_delta se(v)  inherit_dbl_params_from_APS_flag u(1)   update_dbl_params_in_APS_flagu(1)   if (update_dbl_params_in_APS_flag)    aps_dbl_id  if ((!inherit_dbl_params_from_APS_flag) ||  update_dbl_params_in_APS_flag ){    disable_deblocking_filter_flag u(1)    if (!disable_deblocking_filter_flag ) {     beta_offset_div2 se(v)    tc_offset_div2 se(v)    }   }  ..... }

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: decoding a first syntax element defined to indicate whetherdeblocking filter parameters are present in both a picture layerparameter set and a slice header; when the first syntax elementindicates that deblocking filter parameters are present in both thepicture layer parameter set and the slice header, decoding a secondsyntax element in the slice header defined to indicate whether to use afirst set of deblocking filter parameters included in the picture layerparameter set or a second set of deblocking filter parameters includedin the slice header to define a deblocking filter applied to a currentvideo slice; and when the first syntax element indicates that deblockingfilter parameters are not present in both the picture layer parameterset and the slice header, determining that the second syntax element isnot present in the slice header to be decoded.
 2. The method of claim 1,wherein the picture layer parameter set comprises one of a pictureparameter set (PPS) or an adaptation parameter set (APS).
 3. The methodof claim 1, wherein decoding the first syntax element comprises decodingthe first syntax element in one of the picture layer parameter set or asequence parameter set (SPS).
 4. The method of claim 1, furthercomprising, when the first syntax element indicates that deblockingfilter parameters are not present in both the picture layer parameterset and the slice header, defining the deblocking filter applied to thecurrent video slice based on deblocking filter parameters present in oneof the picture layer parameter set and the slice header.
 5. The methodof claim 1, wherein decoding the first syntax element comprises decodingan override enabled flag in the picture layer parameter set thatindicates whether an override of the first set of deblocking filterparameters by the second set of deblocking filter parameters is enabled.6. The method of claim 5, wherein, when the override is enabled,decoding the second syntax element comprises decoding an override flagin the slice header that indicates whether to use the first set ofdeblocking filter parameters from the picture layer parameter set or tooverride the first set of deblocking filter parameters with the secondset of deblocking filter parameters included in the slice header todefine the deblocking filter applied to the current video slice.
 7. Themethod of claim 5, wherein, when the override is not enabled,determining that the second syntax element is not present in the sliceheader comprises determining that an override flag is not present in theslice header to be decoded, further comprising defining the deblockingfilter applied to the current video slice based on the first set ofdeblocking filter parameters included in the picture layer parameterset.
 8. The method of claim 1, wherein decoding the first syntax elementcomprises decoding an inherit enabled flag that indicates whether thefirst set of deblocking filter parameters is present in the picturelayer parameter set to be inherited by the slice header.
 9. The methodof claim 8, wherein, when the first set of deblocking filter parametersis present to be inherited by the slice header, decoding the secondsyntax element comprises decoding an inherit flag in the slice headerthat indicates whether to use the second set of deblocking filterparameters included in the slice header or to inherit the first set ofdeblocking filter parameters from the picture layer parameter set todefine the deblocking filter applied to the current video slice.
 10. Themethod of claim 8, wherein, when the first set of deblocking filterparameters is not present to be inherited by the slice header,determining that the second syntax element is not present in the sliceheader comprises determining that an inherit flag is not present in theslice header to be decoded, further comprising defining the deblockingfilter applied to the current video slice based on the second set ofdeblocking filter parameters included in the slice header.
 11. Themethod of claim 1, further comprising decoding a third syntax elementdefined to indicate that deblocking filter control syntax elements arepresent in the picture layer parameter set and the slice header prior todecoding the first syntax element, wherein the first syntax element andthe second syntax element comprise deblocking filter control syntaxelements.
 12. The method of claim 11, wherein decoding the third syntaxelement comprises decoding a control present syntax element in one ofthe picture layer parameter set and a sequence parameter set (SPS). 13.The method of claim 1, further comprising decoding a fourth syntaxelement defined to indicate that the deblocking filter is enabled forthe current video slice.
 14. The method of claim 13, wherein decodingthe fourth syntax element comprises decoding a deblocking filter enabledflag in a sequence parameter set (SPS) prior to decoding the firstsyntax element.
 15. A video decoding device comprising: a memory thatstores video data; and a processor configured to decode a first syntaxelement defined to indicate whether deblocking filter parameters arepresent in both a picture layer parameter set and a slice header,wherein the processor is configured to, when the first syntax elementindicates that deblocking filter parameters are present in both thepicture layer parameter set and the slice header, decode a second syntaxelement in the slice header defined to indicate whether to use a firstset of deblocking filter parameters included in the picture layerparameter set or a second set of deblocking filter parameters includedin the slice header to define a deblocking filter applied to a currentvideo slice, and wherein the processor is configured to, when the firstsyntax element indicates that deblocking filter parameters are notpresent in both the picture layer parameter set and the slice header,determine that the second syntax element is not present in the sliceheader to be decoded.
 16. The video decoding device of claim 15, whereinthe picture layer parameter set comprises one of a picture parameter set(PPS) or an adaptation parameter set (APS).
 17. The video decodingdevice of claim 15, wherein the processor is configured to decode thefirst syntax element in one of the picture layer parameter set or asequence parameter set (SPS).
 18. The video decoding device of claim 15,wherein the processor is configured to, when the first syntax elementindicates that deblocking filter parameters are not present in both thepicture layer parameter set and the slice header, define the deblockingfilter applied to the current video slice based on deblocking filterparameters present in one of the picture layer parameter set and theslice header.
 19. The video decoding device of claim 15, wherein theprocessor is configured to decode an override enabled flag in thepicture layer parameter set that indicates whether an override of thefirst set of deblocking filter parameters by the second set ofdeblocking filter parameters is enabled.
 20. The video decoding deviceof claim 19, wherein the processor is configured to, when the overrideis enabled, decode an override flag in the slice header that indicateswhether to use the first set of deblocking filter parameters from thepicture layer parameter set or to override the first set of deblockingfilter parameters with the second set of deblocking filter parametersincluded in the slice header to define the deblocking filter applied tothe current video slice.
 21. The video decoding device of claim 19,wherein the processor is configured to, when the override is notenabled, determine that an override flag is not present in the sliceheader to be decoded, and define the deblocking filter applied to thecurrent video slice based on the first set of deblocking filterparameters included in the picture layer parameter set.
 22. The videodecoding device of claim 15, wherein the processor is configured todecode an inherit enabled flag that indicates whether the first set ofdeblocking filter parameters is present in the picture layer parameterset to be inherited by the slice header.
 23. The video decoding deviceof claim 22, wherein the processor is configured to, when the first setof deblocking filter parameters is present to be inherited by the sliceheader, decode an inherit flag in the slice header that indicateswhether to use the second set of deblocking filter parameters includedin the slice header or to inherit the first set of deblocking filterparameters from the picture layer parameter set to define the deblockingfilter applied to the current video slice.
 24. The video decoding deviceof claim 22, wherein the processor is configured to, when the first setof deblocking filter parameters is not present to be inherited by theslice header, determine that an inherit flag is not present in the sliceheader to be decoded, and define the deblocking filter applied to thecurrent video slice based on the second set of deblocking filterparameters included in the slice header.
 25. A video decoding devicecomprising: means for decoding a first syntax element defined toindicate whether deblocking filter parameters are present in both apicture layer parameter set and a slice header; when the first syntaxelement indicates that deblocking filter parameters are present in boththe picture layer parameter set and the slice header, means for decodinga second syntax element in the slice header defined to indicate whetherto use a first set of deblocking filter parameters included in thepicture layer parameter set or a second set of deblocking filterparameters included in the slice header to define a deblocking filterapplied to a current video slice; and when the first syntax elementindicates that deblocking filter parameters are not present in both thepicture layer parameter set and the slice header, means for determiningthat the second syntax element is not present in the slice header to bedecoded.
 26. The video decoding device of claim 25, wherein the picturelayer parameter set comprises a picture parameter set (PPS).
 27. Thevideo decoding device of claim 25, wherein the means for decoding thefirst syntax element comprise means for decoding an override enabledflag in the picture layer parameter set that indicates whether anoverride of the first set of deblocking filter parameters by the secondset of deblocking filter parameters is enabled.
 28. The video decodingdevice of claim 27, wherein, when the override is enabled, the means fordecoding the second syntax element comprise means for decoding anoverride flag in the slice header that indicates whether to use thefirst set of deblocking filter parameters from the picture layerparameter set or to override the first set of deblocking filterparameters with the second set of deblocking filter parameters includedin the slice header to define the deblocking filter applied to thecurrent video slice.
 29. The video decoding device of claim 27, wherein,when the override is not enabled, the means for determining that thesecond syntax element is not present in the slice header comprise meansfor determining that an override flag is not present in the slice headerto be decoded, further comprising means for defining the deblockingfilter applied to the current video slice based on the first set ofdeblocking filter parameters included in the picture layer parameterset.
 30. A computer readable medium comprising instructions for decodingvideo data that when executed cause one or more processors to: decode afirst syntax element defined to indicate whether deblocking filterparameters are present in both a picture layer parameter set and a sliceheader; when the first syntax element indicates that deblocking filterparameters are present in both the picture layer parameter set and theslice header, decode a second syntax element in the slice header definedto indicate whether to use a first set of deblocking filter parametersincluded in the picture layer parameter set or a second set ofdeblocking filter parameters included in the slice header to define adeblocking filter applied to a current video slice; and when the firstsyntax element indicates that deblocking filter parameters are notpresent in both the picture layer parameter set and the slice header,determine that the second syntax element is not present in the sliceheader to be decoded.
 31. A method of encoding video data, the methodcomprising: encoding a first syntax element defined to indicate whetherdeblocking filter parameters are present in both a picture layerparameter set and a slice header; when the first syntax elementindicates that deblocking filter parameters are present in both thepicture layer parameter set and the slice header, encoding a secondsyntax element in the slice header defined to indicate whether to use afirst set of deblocking filter parameters included in the picture layerparameter set or a second set of deblocking filter parameters includedin the slice header to define a deblocking filter applied to a currentvideo slice; and when the first syntax element indicates that deblockingfilter parameters are not present in both the picture layer parameterset and the slice header, eliminating encoding of the second syntaxelement in the slice header.
 32. The method of claim 31, wherein thepicture layer parameter set comprises one of a picture parameter set(PPS) or an adaptation parameter set (APS).
 33. The method of claim 31,wherein encoding the first syntax element comprises encoding the firstsyntax element in one of the picture layer parameter set or a sequenceparameter set (SPS).
 34. The method of claim 31, further comprising,when the first syntax element indicates that deblocking filterparameters are not present in both the picture layer parameter set andthe slice header, defining the deblocking filter applied to the currentvideo slice based on deblocking filter parameters present in one of thepicture layer parameter set and the slice header.
 35. The method ofclaim 31, wherein encoding the first syntax element comprises encodingan override enabled flag in the picture layer parameter set thatindicates whether an override of the first set of deblocking filterparameters by the second set of deblocking filter parameters is enabled.36. The method of claim 35, wherein, when the override is enabled,encoding the second syntax element comprises encoding an override flagin the slice header that indicates whether to use the first set ofdeblocking filter parameters from the picture layer parameter set or tooverride the first set of deblocking filter parameters with the secondset of deblocking filter parameters included in the slice header todefine the deblocking filter applied to the current video slice.
 37. Themethod of claim 35, wherein, when the override is not enabled,eliminating encoding of the second syntax element comprises eliminatingencoding of an override flag in the slice header, further comprisingdefining the deblocking filter applied to the current video slice basedon the first set of deblocking filter parameters included in the picturelayer parameter set.
 38. The method of claim 31, wherein encoding thefirst syntax element comprises encoding an inherit enabled flag thatindicates whether the first set of deblocking filter parameters ispresent in the picture layer parameter set to be inherited by the sliceheader.
 39. The method of claim 38, wherein, when the first set ofdeblocking filter parameters is present to be inherited by the sliceheader, encoding the second syntax element comprises encoding an inheritflag in the slice header that indicates whether to use the second set ofdeblocking filter parameters included in the slice header or to inheritthe first set of deblocking filter parameters from the picture layerparameter set to define the deblocking filter applied to the currentvideo slice.
 40. The method of claim 38, wherein, when the first set ofdeblocking filter parameters is not present to be inherited by the sliceheader, eliminating encoding of the second syntax element compriseseliminating encoding of an inherit flag in the slice header, furthercomprising defining the deblocking filter applied to the current videoslice based on the second set of deblocking filter parameters includedin the slice header.
 41. The method of claim 31, further comprisingencoding a third syntax element defined to indicate that deblockingfilter control syntax elements are present in the picture layerparameter set and the slice header prior to encoding the first syntaxelement, wherein the first syntax element and the second syntax elementcomprise deblocking filter control syntax elements.
 42. The method ofclaim 41, wherein encoding the third syntax element comprises encoding acontrol present syntax element in one of the picture layer parameter setand a sequence parameter set (SPS).
 43. The method of claim 31, furthercomprising encoding a fourth syntax element defined to indicate that thedeblocking filter is enabled for the current video slice.
 44. The methodof claim 43, wherein encoding the fourth syntax element comprisesencoding a deblocking filter enabled flag in a sequence parameter set(SPS) prior to encoding the first syntax element.
 45. A video encodingdevice comprising: a memory that stores video data; and a processorconfigured to encode a first syntax element defined to indicate whetherdeblocking filter parameters are present in both a picture layerparameter set and a slice header, wherein the processor is configuredto, when the first syntax element indicates that deblocking filterparameters are present in both the picture layer parameter set and theslice header, encode a second syntax element in the slice header definedto indicate whether to use a first set of deblocking filter parametersincluded in the picture layer parameter set or a second set ofdeblocking filter parameters included in the slice header to define adeblocking filter applied to a current video slice, and wherein theprocessor is configured to, when the first syntax element indicates thatdeblocking filter parameters are not present in both the picture layerparameter set and the slice header, eliminate encoding of the secondsyntax element in the slice header.
 46. The video encoding device ofclaim 45, wherein the picture layer parameter set comprises one of apicture parameter set (PPS) or an adaptation parameter set (APS). 47.The video encoding device of claim 45, wherein the processor isconfigured to encode the first syntax element in one of the picturelayer parameter set or a sequence parameter set (SPS).
 48. The videoencoding device of claim 45, wherein the processor is configured to,when the first syntax element indicates that deblocking filterparameters are not present in both the picture layer parameter set andthe slice header, define the deblocking filter applied to the currentvideo slice based on deblocking filter parameters present in one of thepicture layer parameter set and the slice header.
 49. The video encodingdevice of claim 45, wherein the processor is configured to encode anoverride enabled flag in the picture layer parameter set that indicateswhether an override of the first set of deblocking filter parameters bythe second set of deblocking filter parameters is enabled.
 50. The videoencoding device of claim 49, wherein the processor is configured to,when the override is enabled, encode an override flag in the sliceheader that indicates whether to use the first set of deblocking filterparameters from the picture layer parameter set or to override the firstset of deblocking filter parameters with the second set of deblockingfilter parameters included in the slice header to define the deblockingfilter applied to the current video slice.
 51. The video encoding deviceof claim 49, wherein the processor is configured to, when the overrideis not enabled, eliminate encoding of an override flag in the sliceheader, and define the deblocking filter applied to the current videoslice based on the first set of deblocking filter parameters included inthe picture layer parameter set.
 52. The video encoding device of claim45, wherein the processor is configured to encode an inherit enabledflag that indicates whether the first set of deblocking filterparameters is present in the picture layer parameter set to be inheritedby the slice header.
 53. The video encoding device of claim 52, whereinthe processor is configured to, when the first set of deblocking filterparameters is present to be inherited by the slice header, encode aninherit flag in the slice header that indicates whether to use thesecond set of deblocking filter parameters included in the slice headeror to inherit the first set of deblocking filter parameters from thepicture layer parameter set to define the deblocking filter applied tothe current video slice.
 54. The video encoding device of claim 52,wherein the processor is configured to, when the first set of deblockingfilter parameters is not present to be inherited by the slice header,eliminate encoding of an inherit flag in the slice header, and definethe deblocking filter applied to the current video slice based on thesecond set of deblocking filter parameters included in the slice header.55. A video encoding device comprising: means for encoding a firstsyntax element defined to indicate whether deblocking filter parametersare present in both a picture layer parameter set and a slice header;when the first syntax element indicates that deblocking filterparameters are present in both the picture layer parameter set and theslice header, means for encoding a second syntax element in the sliceheader defined to indicate whether to use a first set of deblockingfilter parameters included in the picture layer parameter set or asecond set of deblocking filter parameters included in the slice headerto define a deblocking filter applied to a current video slice; and whenthe first syntax element indicates that deblocking filter parameters arenot present in both the picture layer parameter set and the sliceheader, means for eliminating encoding of the second syntax element inthe slice header.
 56. The video encoding device of claim 55, wherein thepicture layer parameter set comprises a picture parameter set (PPS). 57.The video encoding device of claim 55, wherein the means for encodingthe first syntax element comprise means for encoding an override enabledflag in the picture layer parameter set that indicates whether anoverride of the first set of deblocking filter parameters by the secondset of deblocking filter parameters is enabled.
 58. The video encodingdevice of claim 57, wherein, when the override is enabled, the means forencoding the second syntax element comprise means for encoding anoverride flag in the slice header that indicates whether to use thefirst set of deblocking filter parameters from the picture layerparameter set or to override the first set of deblocking filterparameters with the second set of deblocking filter parameters includedin the slice header to define the deblocking filter applied to thecurrent video slice.
 59. The video encoding device 57, wherein, when theoverride is not enabled, the means for eliminating encoding of thesecond syntax element comprise means for eliminating encoding of anoverride flag in the slice header, further comprising means for definingthe deblocking filter applied to the current video slice based on thefirst set of deblocking filter parameters included in the picture layerparameter set.
 60. A computer readable medium comprising instructionsfor encoding video data that when executed cause one or more processorsto: encode a first syntax element defined to indicate whether deblockingfilter parameters are present in both a picture layer parameter set anda slice header; when the first syntax element indicates that deblockingfilter parameters are present in both the picture layer parameter setand the slice header, encode a second syntax element in the slice headerdefined to indicate whether to use a first set of deblocking filterparameters included in the picture layer parameter set or a second setof deblocking filter parameters included in the slice header to define adeblocking filter applied to a current video slice; and when the firstsyntax element indicates that deblocking filter parameters are notpresent in both the picture layer parameter set and the slice header,eliminate encoding of the second syntax element in the slice header.